Chemical Reactions Third Assignment Name ______

Chemical energy sources are often portable and provide large amounts of energy. Fossil fuels are one kind of chemical energy source. Most of the energy we use in the United States is generated by the combustion of fossil fuels. However, fossil fuel combustion adds greenhouse gases to the atmosphere, mostly CO2. One measure of the total amount of greenhouse gases that are emitted into the atmosphere each year is called a carbon footprint. Read this article to compare the carbon footprint of an average person in the United States to an average person around the world.

Whether you live in a cardboard box or a luxurious mansion, whether you subsist on homegrown vegetables or wolf down imported steaks, whether you're a jet-setter or a sedentary retiree, anyone who lives in the U.S. contributes more than twice as much greenhouse gas to the atmosphere as the global average, an MIT class has estimated.

The class studied the carbon emissions of Americans in a wide variety of lifestyles--from the homeless to multimillionaires, from Buddhist monks to soccer moms--and compared them to those of other nations. The somewhat disquieting bottom line is that in the United States, even people with the lowest energy usage account for, on average, more than double the global per-capita carbon emission. And those emissions rise steeply from that minimum as people's income increases.

"Regardless of income, there is a certain floor below which the individual carbon footprint of a person in the U.S. will not drop," says Timothy Gutowski, professor of mechanical engineering, who taught the class that calculated the rates of carbon emissions. The results will be presented this May at the IEEE International Symposium on Electronics and the Environment in San Francisco.

While it may seem surprising that even people whose lifestyles don't appear extravagant--the homeless, monks, children--are responsible for significant greenhouse gas emissions, one major factor is the array of government services that are available to everyone in the United States. These basic services-- including police, roads, libraries, the court system and the military--were allocated equally to everyone in the country in this study. Other services that are more specific, such as education or Medicare, were allocated only to those who actually make use of them.

The students conducted detailed interviews or made detailed estimates of the energy usage of 18 lifestyles, spanning the gamut from a vegetarian college student and a 5-year-old up to the ultrarich-- Oprah Winfrey and Bill Gates. The energy impact for the rich was estimated from published sources, while all the others were based on direct interviews. The average annual carbon dioxide emissions per person, they found, was 20 metric tons, compared to a world average of four tons.

But the "floor" below which nobody in the U.S. can reach, no matter a person's energy choices, turned out to be 8.5 tons, the class found. That was the emissions calculated for a homeless person who ate in soup kitchens and slept in homeless shelters.

The analysis was carried out by Gutowski and 21 students in his 2007 class, "Environmentally benign design and manufacturing." They derived a system for making such comparisons, which they call ELSA-- environmental life style analysis.

Unlike some other attempts to quantify carbon-emission rates, Gutowski and his students took great care to account for often-overlooked factors, such as the "rebound effect." That's when someone makes a particular choice--for example, buying a hybrid car instead of a gas-guzzler--but then uses the money saved from their reduced gasoline costs to do something else, such as taking a long trip by airplane. The net impact, in such a case, may actually be an overall increase in carbon emissions.

"When you save energy, you save money," Gutowski explains. "The question is, how are you going to spend that money?"

The students looked at the factors within each person's control that might lead to a reduction in carbon output. They found that achieving significant reductions for the most part required drastic changes that would likely be unacceptable to most people. As a result, they said, "this all suggests to us very significant limits to voluntary actions to reduce impacts, both at a personal level and at a national level."

In a continuation of the class this semester, another group of students are exploring this question in more detail, looking at just what kinds of things people really can do to limit their environmental impact. The question they are addressing, Gutowski says, is "can average Americans tighten their belts" in a way that would make a significant difference? Once again, the class will be interviewing people living i n a wide variety of ways, including an Amish farming lifestyle. Then, after analyzing the results and possible changes, they will go back to the same people and ask, "Would you consider these alternatives?"

In general, spending money on travel or on goods that have substantial energy costs in their manufacture and delivery adds to a person's carbon footprint, while expenditures on locally based labor-intensive services--whether it's going to a therapist, taking an art class, or getting a massage--leads to a smaller footprint.

But the biggest factors in most people's lives were the obvious energy-users: housing, transportation and food. "The simple way you get people's carbon use down is to tax it," Gutowski says. "That's a hard pill to swallow--politicians don't like to step up" to support such measures. Absent such national actions, he says, it is important to study "what role consumer choices can play" in lowering the nation's carbon emissions.

If nothing else, the members of this class got a whole new perspective. "The students really got into it," Gutowski says. "It raised everybody's awareness about the issues."

Knowing that greenhouse gases are contributing to climate change, how can we reduce our carbon footprint, particularly in the United States? Could hydrogen fuel replace fossil fuels in the future? Why or why not? Should the size of a person’s carbon footprint be limited by law? Why or why not?

Warm-Up

If we pass electric current through water using two electrodes, a chemical reaction occurs. The water breaks down into two different substances: hydrogen gas and oxygen gas. Bubbles of each gas form at the two electrodes. We can collect the gases and reverse the reaction easily. When we light the mixture of gases with a spark, they burn and form a single product, water.

What Is a Chemical Reaction?

We can’t explain all of the events taking place around us. One kind of event that is hard to explain is a chemical reaction. In a chemical reaction, original substances undergo a complete change into new substances. This change in substances fascinated early scientists because they couldn’t understand them.

Henry Cavendish was an early chemical experimenter who carried out chemical reactions in his lab. During his experiments, Cavendish discovered hydrogen gas and tested its properties. He found that hydrogen burns in air to produce water and that the density of hydrogen is lighter than air.

Chemical Reactions and Substances People are fascinated with chemical reactions because they help us find and create new substances. As a result, people have identified over 50 million substances. All these substances are made of just 92 elements! Most substances are compounds that include more than one kind of atom. Many chemical reactions result in compounds. Some of these compounds, such as water and carbon dioxide, are made naturally. They form because of chemical reactions that occur in living organisms and during natural occurrences such as volcanoes and lightning. Other compounds are synthetic. They’ve been made in chemical reactions carried out by scientists. Synthetic compounds include plastics, medicines, and preservatives.

Describing Chemical Reactions

Building an erupting volcano is a popular science project. Adding baking soda (solid) to vinegar (liquid), gives us carbon dioxide (gas). This gas rises up in the form of bubbles and looks like an erupting volcano as it flows out. Here, the original substances, baking soda and vinegar, are reactants. The new substance, carbon dioxide, is the product. We can describe this chemical reaction using a chemical equation in words: baking soda + vinegar → carbon dioxide + unknown substances

A reddish layer of rust can form on old iron nails and bikes. In this chemical reaction, iron reacts slowly with oxygen in the air. The chemical name for rust is iron oxide. What are the reactant(s) and product(s) of this reaction? Write down the equation, in words, for the formation of rust.

A chemical equation is a powerful tool that we can use to write a chemical reaction in words. The substances can be described using everyday names or scientific names. For example, here’s the equation for baking soda and vinegar using chemical names: acetic acid + sodium bicarbonate → carbon dioxide + sodium acetate

We can also write a chemical equation using chemical formulas. Chemical formulas are a symbolic way to write substances. Every substance has a chemical formula. For example, the formula for water is H 2O, and the formula for carbon dioxide is CO2. Evidence of Chemical Reactions

In the experiment Cavendish performed, a metal (solid) and an acid (liquid) reacted to produce a gas. In any chemical reaction, substances interact with each other to give new substances that have different properties. In the Cavendish experiment, the product, which is the gas, has properties that are different from the properties of the reactants.

Release of a gas can mean that a chemical reaction has taken place. When carrying out a possible chemical reaction in the lab, watch for such clues. There are four different clues that indicate a chemical reaction has taken place. They are a change in color or temperature, release of a gas, or production of a precipitate.

Sometimes, observing clues, such as a change in color or temperature, doesn’t confirm that a chemical reaction has taken place. For example, adding a drop of red ink to a glass of water changes the color of the water. However, no chemical reaction has taken place. To definitively determine that a chemical reaction has taken place, it is necessary to carefully test the properties of reactants and products. Each substance has a unique set of properties. One of them is density. We can determine whether two substances are the same or different by calculating and comparing their densities. No two substances in their purest form have the same density.

Changes in Matter

We can classify all the changes of matter around us into two main kinds: physical changes and chemical reactions. Physical changes include mixing, separating, and changes in state. No chemical reaction takes place in this kind of change, and it does not result in new substances. On the other hand, a chemical reaction results in new substances (products).

It’s not always easy to determine what kind of change of matter is occurring. For example, when we heat water, bubbles form when the water reaches its boiling point. So, we may think that water has decomposed and the bubbles contain oxygen and hydrogen gases. However, those bubbles are just water vapor, which is not a new substance. Heating the water resulted only in a change of state.

If two substances are components of a mixture, they retain their individual properties. They have not reacted with each other. We can separate the substances of a mixture using simple methods. For example, we can easily separate zinc and aluminum pieces from a mixture of metals with a pair of tweezers. This process of separating is a physical change.

In some cases, it can be difficult to tell whether two combined substances have mixed or reacted. For example, when we add sugar to water, sugar disappears. It might seem that there is a chemical reaction between the two. Actually, it’s just a mixture.

In the real world, many phenomena include both physical changes and chemical reactions. It can be difficult to analyze these phenomena. Suppose we make a solution of sugar and water and heat it. Water evaporates—this is a physical change. But over time, the sugar might begin to burn—this is a chemical reaction. Recipes for making caramel depend on this burning process. Sometimes, we can’t clearly define certain changes of matter as either a physical change or a chemical reaction. Likewise, not all chemical changes are the same. Let’s examine some different kinds of chemical reactions.

Types of Chemical Reactions

Chemists have categorized chemical reactions. In this section, we’ll examine four different kinds of chemical reactions: synthesis reactions decomposition reactions combustion reactions replacement reactions

Synthesis Reactions

In a synthesis reaction, two or more substances react to produce a new compound. Some synthesis reactions occur between two elements. One common reactive element is oxygen. Oxygen reacts with many elements to produce compounds. Rusting and tarnishing are two examples of synthesis reactions. In both cases, oxygen reacts with metal elements. In rusting, the metal is iron, and in tarnishing, the metal is silver, copper, or aluminum.

A synthesis reaction can also occur between an element and a compound and between two compounds.

Decomposition Reactions

The opposite of a synthesis reaction is a decomposition reaction. In this kind of reaction, a compound breaks down into elements or into simpler compounds.

Decomposition reactions often require external energy such as heat, light, or electricity. That’s because the products of a decomposition reaction have more energy than the reactant. So, we need to add energy to the reactant.

Electricity is a common form of energy used for decomposition. In labs, chemists use batteries to decompose compounds. Batteries help chemists determine whether a substance is a compound or an element. Electrolysis of water is an example of a decomposition reaction. Electrolysis is the use of electricity to cause a chemical change. In this case, electrolysis decomposes water into oxygen and hydrogen.

Combustion Reactions

Burning is a combustion reaction. This reaction occurs when a substance reacts with oxygen. A combustion reaction produces a lot of energy in addition to chemical products.

Many common substances that burn—such as wood, paper, natural gas, coal, wax, gasoline, and oil— are made primarily of atoms of carbon and hydrogen. When we burn these substances, carbon and hydrogen react with oxygen to produce carbon dioxide and water. Usually, water is released in the form of water vapor. When the water vapor cools, it changes into liquid water.

Combustion reactions need a small amount of external energy to start. This external energy is called ignition. (One common example is the ignition of gas in cars.) Each substance burns at or above a specific temperature, which is its ignition point.

The amount of energy released in a combustion reaction is much greater than the energy needed to start it. The products of a combustion reaction have less energy than the reactants, which is why energy is released. The energy released in a combustion reaction can also speed up the reaction. In some cases, this leads to an explosion. Combustion of fossil fuels such as coal and gas is the primary source of energy in our day-to-day lives.

Replacement Reactions

A replacement reaction has two reactants and two products. In this kind of reaction, atoms from one reactant replace the atoms in the other reactant.

Cavendish’s experiment, which we saw earlier, is an example of a replacement reaction: hydrochloric acid + zinc → zinc chloride + hydrogen

The word chemical equation shows that the zinc replaced the hydrogen in the hydrochloric acid. The products, therefore, are hydrogen and zinc chloride.

Another example of a replacement reaction is neutralization. In a neutralization reaction, an acid and an alkali react to form water and a salt. A person who has stomach acidity might take an antacid. An antacid is an alkali, and it reacts with excess stomach acid. This reduces, or neutralizes, the acid in the stomach.

Science in the News:

Smart Materials

How is all this knowledge of chemical reactions helping us in the modern world? Well, engineers and scientists are always trying to create smart devices and materials that anticipate our needs. For instance, it seems that smart phones get “smarter” every few months. Scientists have also developed smart materials that change their color or form in response to a stimulus. Another smart material is a shape-memory material. This material can change its shape when heated, cooled or exposed to light, but then returns to its original shape.

Complete the activity on the next screen to learn more about a smart material that can heal, or repair, itself.

WASHINGTON, D.C. — A scratch on your brand new car can be expensive to fix. A teen has helped to make a new plastic that might do more than protect your bumper: It could make small scratches disappear.

Emily Spencer, 18, helped create a plastic that heals itself under ultraviolet light. The material could be used one day to make everything from scratch-proof eyeglass lenses to the door panels and fenders of your next car.

A senior at Hathaway Brown School in Shaker Heights, Ohio, Emily presented her project at the Intel Science Talent Search. The annual event is run by Society for Science & the Public and sponsored by Intel. It brings 40 high school students here to show off their research and to compete for cash awards of up to $150,000 each.

Emily loves thinking about the materials that make up the objects we use every day. “You can look at something like your phone case, and it’s just an object,” she says. People tend to overlook the materials that go into making such objects, she notes. But “we can improve those things and make them better.” Working with a graduate student in a nearby lab at Case Western Reserve University in Cleveland, Emily developed a new kind of polymer — a material made of long chains of repeating groups of atoms. It looks like a “really thick sort of yellowish plastic wrap,” but it’s far more than that. When Emily’s plastic is scratched, it can heal itself.

All it needs is a quick burst of ultraviolet (UV) light — a part of the light spectrum that is invisible to the human eye. Place a piece of her plastic, scratched with a razor blade, under a UV lamp. The scratch heals while you watch. The healed plastic is just as strong as the original.

The plastic also has a feature called shape memory. A flat piece can be heated and twisted into a new shape, such as a spiral. It holds that new shape when the plastic is cool. But heat it again, and the material returns to its original, flat shape.

“It’s sort of like hair,” Emily explains. “If my hair is naturally curly and I iron it straight, it will hold the straight shape. But my hair won’t be straight forever. It will ‘remember’ that it’s curly. It will go back to being curly when it’s exposed to water.” She was part of a team that published details on the design of the new plastic in a scientific journal in 2013. The plastic is a smart material — one that can change when scientists apply stress, heat or water. The material’s flexibility comes from links between the repeating groups of atoms that make up the polymer. Its healing powers come from atoms of sulfur in the plastic. The sulfur atoms bond to each other to form a disulfide bond, holding the plastic in a particular shape. But under UV light, those sulfurs break apart.

“When the bonds break with the UV light, the material becomes kind of flowy,” Emily explains. “It can flow into cracks and imperfections in the material,” healing scratches. Turn off the UV light, and the sulfurs bond together again. Meanwhile, the scratches are gone.

All those sulfur atoms made a nasty stink in the lab. “The reaction [to make the material] smells like rotten eggs,” the teen notes. “I kept apologizing to people in the lab for the smell.”

Emily would like to be able to apply materials like hers to objects such as cars. “If you had your car coated [with the plastic] and then it got scratched, you could first use the heat to activate the shape memory to bring the pieces closer together,” she notes. “Then you could use the UV light to heal the leftover scratches.” This material, and others like it, might one day make those expensive scratches a thing of the past.

Power Words atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

bond (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation. disulfide A pair of sulfur atoms linked together. Intel Science Talent Search An annual competition run by Society for Science & the Public and sponsored by Intel. It brings 40 high-achieving high school seniors to Washington, D.C. to show their research projects to the public and to compete for awards. journal (in science) A publication in which scientists share their research findings with the public. Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send out all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work. peer review (in science) A process in which scientists in a field carefully read and critique the work of their peers before it is published in a scientific journal. Peer review helps to prevent sloppy science and bad mistakes from being published. plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation. polymer Substances whose molecules are made of long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example). shape memory polymer A smart material made of long chains of repeating atoms. It has the ability to take a new shape and then return to a former shape when light, heat or some other stimulus is applied. smart material Materials designed by researchers to change in a controlled way when triggered by a certain temperature, stress, moisture or other stimulus. stress (in biology) A factor, such as unusual temperatures, moisture or pollution, that affects the health of a species or ecosystem. (in physics) Pressure or tension exerted on a material object. ultraviolet A portion of the light spectrum that is close to violet but invisible to the human eye.

What is unusual about the material that Emily invented?

5 The chemical name for laughing gas is dinitrogen oxide. The two elements found in a sample of this gas are ______and ______.

6 In certain fireworks, potassium nitrate breaks down into potassium oxide, nitrogen, and oxygen. This is an example of a ______reaction. The opposite process is a______reaction.

7 Which images show chemical reactions?

8 Identify the type of chemical reaction that is described.

Warm-Up

Ryan works at a deli. One day, his younger sister, Meg, visited him at the deli and happened to look at his notebook. She couldn’t understand Ryan’s entries. She saw W2C, W2V, R3H4Ch, and R2C2V. Ryan explained that he used a code for the sandwiches and other items he sold. For example, W meant wheat bread, and the subscript 2 meant two slices. C meant chicken. Meg spent a little time figuring out the meaning of each symbol. It was a lot of fun!

Representing Substances at the Atomic Level

In chemistry, substances are observed and their properties are measured. All substances consist of elements, and elements consist of atoms. There are 92 elements found in nature. These elements combine in various ways to form other substances. More than a million substances are found on Earth. To make it easier to understand these combinations, scientists have given each element a symbol.

Complete the following activity to learn how scientists use symbols and pictures to show the atoms in a substance.

The drawing shows different ways to present information about atoms in a substance. The three representations are a chemical formula, a picture, and a name. The substance is carbon dioxide, a colorless gas found in the atmosphere.

One way to represent a substance is with a chemical formula. In the formula CO2, what do the symbols C and O refer to?

In the formula CO2, what does the subscript 2 after the O mean?

Another way to represent a substance is with a picture. What information does the picture provide about carbon dioxide?

Chemical Formulas of Substances

Let’s review how chemical formulas show substances at the atomic level. A chemical formula tells us which atoms are present in the substance and in what ratio. Each atom comes from a specific element and is shown with a symbol. The periodic table lists the elements and their symbols.

In many substances, a molecule is the smallest particle in the substance. Many chemical formulas show a molecule. For example, the chemical formula for water is H2O. The H stands for hydrogen, and the O stands for oxygen. The subscript 2 after the H means that there are two atoms of hydrogen. The absence of a subscript after the O means that there’s only one atom of oxygen. The chemical formula tells us that a molecule of water has two hydrogen atoms and one oxygen atom.

Images of Substances

Substances at the atomic level can also be shown with images. This image shows a molecule of water, which has the chemical formula H2O. Try to identify which part of the image indicates H and which part indicates O.

Like chemical formulas, images show the types and ratios of atoms in substances. Different shapes and colors can be used to represent the types of atoms in a substance. But images also show additional information. They show the chemical bonds that connect a substance’s atoms. Let’s look at images of two substances: water and salt.

The image on the left shows water, which has the chemical formula H2O. Water is made up of separate molecules. The image on the right shows table salt. Table salt’s chemical name is sodium chloride. Its formula is NaCl. It has two kinds of atoms: sodium and chlorine. Unlike water, all the atoms in sodium chloride are connected. They form a network.

Many liquid and gaseous substances, including water, are molecular. Most solid substances are networks. All of their atoms are connected. Let’s look at some more examples of substances.

Different substances might have the same atoms, but they are combined in different ratios. The chemical formula for carbon dioxide is CO2, and the chemical formula for carbon monoxide is CO. There is a difference of one atom of oxygen in their molecular structure. So, the two gases have different properties. Carbon dioxide is used by plants and is essential for life. Carbon monox ide is a deadly gas.

Representing Chemical Reactions

When early chemists performed chemical reactions, they didn’t know what was happening at the atomic level. However, they found that substances reacted in set ratios. For example, in the reaction of hydrogen and oxygen to make water, chemists observed that the gases reacted in the ratio 2 to 1. If they tried to react four liters of hydrogen with 1 liter of oxygen, only two liters of hydrogen would react. Two liters of hydrogen would be left over at the end of the reaction.

Balanced Chemical Equations We can describe a chemical reaction with words. We can also describe a chemical reaction with a chemical equation. For example, this chemical equation represents the synthesis of carbon dioxide from carbon and oxygen:

C + O2 → CO2

Here, C and O2 are the reactants and CO2 is the product. Notice in the equation that there’s one atom of C and two atoms of O in the reactants and in the product. A chemical equation with chemical formulas should be balanced. It should have the same numbers and kinds of atoms on each side of the arrow.

In some equations, we need to use coefficients in front of a chemical formula to balance the chemical equation. Here’s the balanced chemical equation for the combustion of methane. The reactants are methane and oxygen, and the products are carbon dioxide and water. Notice the coefficient 2 in front of oxygen and water in the equation:

CH4 + 2O2 → CO2 + 2H2O

The image shows how to count the atoms in the chemical equation for the combustion of methane to find out whether it’s balanced. There’s one atom of carbon, four atoms of hydrogen, and four atoms of oxygen in the reactants. The product also has the same numbers and kinds of atoms. So, the equation is balanced. Complete the activity on the next screen to see step-by-step how to check whether a chemical equation is balanced.

In this activity, you’ll draw and count atoms to understand how nitrogen and hydrogen react to make ammonia. Begin by studying this chemical equation: N2 + 3H2 → 2NH3. Then answer the following questions.

Draw the reactants. Keep in mind that one molecule of nitrogen has two bonded atoms, and one molecule of hydrogen has two bonded atoms.

Count the nitrogen and hydrogen atoms in the reactants. How many of each kind of atom are there?

Draw the atoms in the two molecules of ammonia, which are the products.

Count the nitrogen and hydrogen atoms in the drawing of the products. How many of each kind of atom are there?

Law of Conservation of Mass

Early chemists found that the mass of a system at the beginning of an experiment was the same at the end of the experiment. This discovery led to the conclusion that during an experiment, no new matter is created and no matter is destroyed. This principle is often referred to as the law of conservation of mass. A balanced chemical equation reflects the law of conservation of mass.

Careers in Science: Nanotechnology

Nanotechnology is a new type of chemistry. In nanotechnology, people create tiny structures made of atoms. How tiny? Well, consider that a sheet of newspaper is 100,000 nanometers thick—that’ll provide some idea of the scale of these tiny structures.

In nanotechnology, people manipulate atoms at a very small scale. The tiny structures that are made can’t be seen by the naked eye.

There are many different kinds of nanostructures. One kind of structure is a very small tube, which is called a nanotube.

Nanostructures are made in labs called clean rooms. These special labs prevent contamination from people’s bodies or clothes. This precaution is necessary because the structures are very small—even a speck of dust might alter the product.

Scientists use nanotechnology to make many products. Here are a few: ultra-black coating that absorbs all light miniature fibers that lengthen and shrink to build very small artificial muscles for tiny robots nanotube sponges that soak up oil spills nanotube containers that deliver drugs directly to cells in the human body

Nanotechnology Careers

For people who would like to work in nanotechnology, there are a few career options. Technicians operate specialized equipment, and produce, test, and modify nanomaterials. Engineers in the field of nanotechnology develop and test new products that use nanostructures. Research scientists make new kinds of nanostructures.

Calcium carbonate is a compound that is used to make chalk for drawing on rocks or pavement. One molecule has one atom of calcium (Ca), one atom of carbon (C), and three atoms of oxygen (O). Which is the correct way to write the chemical formula for calcium carbonate?

A. 3CaCO

B. Ca3CO

C. CaCO3

D. Ca3C3O3

Sodium bicarbonate is the chemical name for baking powder. Its chemical formula is NaHCO 3. What does the subscript 3 mean? A. There are three molecules of sodium bicarbonate.

B. There are three molecules of oxygen in sodium bicarbonate.

C. There are three atoms of oxygen in sodium bicarbonate.

D. There are three atoms of sodium bicarbonate.

Warm-Up

There’s a lot of chemistry involved in fireworks. When ignited, the substances in fireworks chemically react and release energy in the form of heat, light, and sound. But fireworks aren’t unique. The release or absorption of energy is part of every chemical reaction.

Chemical Reactions and Energy

Energy is something that moves or changes matter. Energy exists in many different forms, including chemical energy. Every substance has a specific amount of chemical energy. In some reactions, some chemical energy is transformed into other forms of energy. For example, when substances burn, the reaction releases heat and light energy. The chemical name for burning is combustion. This type of reaction occurs when oxygen reacts with a substance and releases a large amount of energy in the form of heat and light. Energy released during the combustion of fossil fuels is the main source of energy for vehicles and electricity generation. reactions.

Chemical Reactions Release and Absorb Energy

In addition to combustion, several other reactions release energy. Respiration is one of these reactions. Energy is released when glucose (sugar) reacts with oxygen in the body’s cells. Our bodies use the energy released for various activities. Another type of reaction is called an electrochemical reaction. This kind of reaction occurs inside a battery, for example. The energy released by the reaction is in the form of an electric current. Reactions that release energy to the surroundings are called as exothermic reactions. Some chemical reactions absorb energy. During photosynthesis, plants absorb energy from sunlight to make food from carbon dioxide and water. Oxygen and glucose are the products of this reaction. Activating a cold pack starts a reaction that absorbs heat. Baking and most other cooking processes involve reactions that absorb heat. Reactions that absorb energy from the surrounding are called as endothermic reactions.

Describing Energy in Chemical Reactions In a chemical reaction, one set of substances (reactants) are broken down or combined to form another set of substances (products). We’ve seen that energy is released or absorbed in chemical reactions.

But the total amount of energy in a chemical reaction remains the same. So, energy is just transferred from one form to another. This outcome is based on the law of conservation of energy. This law states that energy is neither created nor destroyed. This law holds true for any form of energy.

Chemists have proven this law for chemical reactions over and over again. They’ve found that the energy released or absorbed is always in the same proportions for a given reaction. This outcome is true even if a reaction occurs faster, as shown in the combustion video. The amount of energy released or absorbed doesn’t depend on the rate of reaction. The change in energy is related only to the chemical energy of the substances in the reaction.

In addition to the energy released or absorbed, all reactions need energy to start. This energy is called activation energy. Let’s take a closer look at chemical energy and activation energy.

Chemical Energy

Every substance has chemical energy. Chemical energy is the energy that substances possess because of the way their atoms are grouped together. The value of chemical energy is different for different substances.

The chemical energy of substances explains why energy is released or absorbed in a chemical reaction. The difference in the amounts of chemical energy of reactants and products determines whether energy is absorbed or released. If reactants have more chemical energy than products, energy is released. If reactants have less chemical energy than products, energy is absorbed.

When a carbon monoxide molecule collides with a nitrogen dioxide molecule, the atoms rearrange to form the products carbon dioxide and nitrogen oxide.

Activation Energy All chemical reactions need a certain amount of energy to begin. This energy is called activation energy. For example, to start a car engine, fuel needs to be ignited. The activation energy is often thermal energy, but it can also be any other form of energy. The amount of activation energy needed is always the same for a particular reaction, unless a catalyst is used. A catalyst is a special substance that lowers activation energy. Why is activation energy needed? Activation energy increases the temperature of the reactants. This higher temperature raises the kinetic energy of particles in the reactants. The particles move faster and collide with each other with enough energy to enter a transition state. The transition state is a phase of a chemical reaction. In the transition state, existing bonds between atoms break and new bonds form. The result is the particles in the products.

Reaction Energy Diagrams

A reaction energy diagram shows the process of a chemical reaction in terms of energy. The images show these energy values: energy of the reactants energy of the transition state energy of the products

Activation energy and the change in chemical energy can be determined from the diagram. Activation energy is the difference in energy between the reactants and the transition state. The chemical energy released or absorbed is the difference in energy between the reactants and products. The two diagrams show a reaction that releases energy and a reaction that absorbs energy. The diagrams have different shapes. In the reaction in Diagram 1, energy is released. The products have low energy compared with the reactants. In the reaction in Diagram 2, energy is absorbed. The products have high energy compared with the reactants.

Science in the News: Hydrogen-Powered Vehicles

Today, combustion of fossil fuels fulfills almost all of our energy needs. However, these fuels can be hazardous to our environment. Fossil fuels produce carbon dioxide during combustion. Excess carbon dioxide has been linked to climate change. Fossil fuels also create pollution, adding harmful substances to the environment. During combustion, fossil fuels produce acids in the atmosphere. The acids are formed from impurities such as sulfur. These acids mix with soil and water and can have harmful effects. Both climate change and acid pollutants can make some parts of the environment unsuitable for the organisms that live there.

Fossil fuels aren’t a renewable energy source. Eventually, they’ll be used up. To address this problem, scientists are looking for alternatives to fossil fuels. They’ve discovered that hydrogen can be used as a fuel. Some people believe that hydrogen will replace fossil fuels in the future. One fossil fuel is methane, the main component of natural gas. In the following activity, you’ll compare the combustion of methane with the combustion of hydrogen. You’ll see why hydrogen is being considered as an alternative fuel. Study the balanced chemical equations for the reactions of methane (CH4) with oxygen and hydrogen with oxygen. Methane is the main component of fossil fuels such as natural gas.

CH4 + 2O2 → CO2 + 2H2O + energy

2H2 + O2 → 2H2O + energy What product of the reaction of methane has an impact on the environment?

Does the reaction of hydrogen produce any products that negatively affect the environment?

What is similar about the energy changes in the two reactions?

Advantages of Hydrogen Fuel

When hydrogen combines with oxygen, it produces a lot of energy. Water is the only product of this reaction. The water produced in this reaction can be broken down to create hydrogen fuel. The main advantage of using hydrogen is that it doesn’t produce carbon dioxide or any pollutants that f orm acids. Using hydrogen as a fuel has fewer negative effects on the environment than using fossil fuels.

Another advantage of hydrogen fuel is that it doesn’t have to be burned. Hydrogen can react with oxygen in a special type of battery called a fuel cell. Vehicles that use these batteries are called fuel cell vehicles (FCV). The fuel cell is more efficient than combustion. Starting with the same amount of fuel, a fuel cell car can go twice as far as a car that uses fossil fuel.

The Challenge of Obtaining Hydrogen A hydrogen fuel cell produces enough electricity to power an electric car. These cells can produce electricity for use in homes too. Fuel cells are quite useful because they’re portable, which means they can be easily moved from place to place. The cells can be used anywhere. The current electricity system isn’t as flexible because it requires connection to the electric grid.

On the other hand, pure hydrogen is a rare gas. Its availability is limited. One possible way to get hydrogen is to decompose water (H2O). Scientists are working to find a catalyst that will lower the activation energy needed to decompose water. The Sun could decompose water into hydrogen if the activation energy dropped low enough. Because solar energy is a renewable resource, this method could be a beneficial way to get hydrogen.

Warm-Up

Have you ever heard of paint that changes color to match its surroundings? Or clothing that generates electricity when a person moves—enough to charge a cell phone? These aren’t make-believe products from a TV show. They’re synthetic materials that scientists have developed in laboratories.

If you could make a new material for use in clothing, vehicles, sports equipment, grooming, or construction, what would you make?

What special properties would the material have?

What purpose would it serve?

What Are Synthetic Materials?

Since before recorded history, people have used natural materials to make buildings, clothing, containers, and tools. Natural materials include stone, wicker, wood, bone, cotton, leather, and silk. People used each of these materials depending on their properties. Over time, people learned how to apply their knowledge to make new materials that better suited their needs. These new materials are called human-made materials, or synthetic materials.

So what are synthetic materials, and how do we make them? Synthetic materials aren’t available in nature, but we use natural resources to make them. Today, most of the materials we use are synthetic materials. There are four main types of synthetic materials.

Activity

In this activity, you’ll describe the pros and cons of the properties of different materials used to make cups. For each material, consider the following aspects of its performance: how it feels how it affects taste how it looks how easily it breaks how easily it dents its weight how easily it can be cleaned whether it stains with use

Consider a cup made of plastic. What are the pros of using plastic?

What are the cons of using a cup made of plastic?

Most plates, bowls, and cups are made from a synthetic material called ceramic, which is also called china. It’s usually painted and can break if dropped. Consider a cup made of ceramic. What are the pros of using ceramic?

What are cons of using a cup made of ceramic?

Consider a cup made of steel. What are the pros of using steel?

What are the cons of using a cup made of steel?

A major camping retailer is marketing a cup that’s made of a composite material. A composite is a combination of materials. In this example, the cup is made of wood and plastic. The retailer says that this material is more durable than plastic and that it won’t break or dent. The material is light, it looks and feels nice, it doesn’t affect taste, and it’s easy to clean. In terms of properties, what’s the value of making composite materials?

The camping retailer also says its composite cup can be easily recycled. Why would this aspect of the material be important to some people?

Based on this activity, which cup would you purchase? Explain the reason for your decision.

The four main types of synthetic materials are polymers, ceramics, alloys, and composites. The materials from the activity—plastic, ceramic, steel, and a composite material—are synthetic materials.

The study of how to develop and process synthetic materials is called materials science. Materials science is a branch of physical science. In the image, the technician is rolling steel sheets in a way that gives the metal desirable properties.

Polymers

Polymers are substances with relatively large molecules. There are two kinds of polymers—natural polymers and synthetic polymers. Natural polymers come from living organisms. Some synthetic materials are made by processing natural polymers. For example, paper products are made from processed cellulose, a natural plant polymer. The synthetic fabric rayon is also made from processed cellulose.

People also make synthetic polymers using chemical reactions. Oil and natural gas, two nonrenewable resources, are the starting materials for synthetic polymers. Plastics and fabrics such as nylon and polyester are synthetic polymers. Polymers, and plastics in particular, are used in many products. Take a look around. Plastics are a part of most of the products we use.

There are many reasons we use plastic to make so many items. We can shape plastic into any form or texture. Plastic is also lightweight, strong, and durable. Because plastic repels water, it can be used outdoors and to wrap food items. It’s also a good insulator, which means it doesn’t conduct heat or electricity. This characteristic is why most pans have plastic handles. In electronic cords and electronics devices, plastic insulates wires and small circuits and protects people.

When plastics are made, a change in the starting material or reaction conditions results in different kinds of plastic. Different kinds of plastic vary in terms of density, flexibility, elasticity, and hardness. We wrap food items with soft, stretchy plastic. Hard, strong plastic is used to make chairs. All of these features of plastic and its relatively low cost make it a widely used material.

Ceramics

Many items that we use in our daily lives, such as dishes, bricks, tiles, and glass, are made of ceramic. Bone and tooth replacements and strong cutting tools are also made of ceramic. Ceramic coatings are also used on metals. People make ceramics by heating natural materials such as clay and sand at very high temperatures.

Some ceramics are the hardest materials in the world. Ceramics are light, durable, brittle, and often slippery. Some ceramic dishes are microwave- and oven-safe because they can withstand high heat. Most ceramics are good insulators, so they don’t conduct heat and electricity. However, some speci al kinds of ceramics are conductors. One kind of ceramic is even magnetic, which is a very rare property.

Alloys Pure metals are very soft. To make a pure metal more useful, we heat it and mix in other elements. This process is called alloying, and the product is a metal alloy. A metal alloy is harder and less reactive than a pure metal. Alloys are also good conductors of heat and electricity. An alloy has a base metal and one or more alloying components. Alloying components are metallic or nonmetallic elements that are usually present in very small quantities compared with the base metal. Steel, sterling silver, chrome, brass, and bronze are all alloys. Let’s take a look at how some of these alloys are made.

Composites

Composites are combinations of different materials. A composite blends the desirable properties of each of its components. Sometimes, a composite even has new properties not seen in any of its components.

Concrete and plywood are composites. Concrete is a mixture of sand, cement, and other granular additives. Plywood is a combination of thin wooden sheets glued together. Another common composite is fiberglass, which is strong and light. It’s a combination of plastic and fine glass fibers. Cars, boats, planes, and surfboards have fiberglass in their bodies. Impact of Synthetic Materials

How do all of these synthetic materials affect our lives? It’s clear that they make our modern world possible. In many cases, people find that synthetic materials are much more effective than natural materials.

Electronic devices such as cell phones, tablets, and laptops are all made of synthetic materials. Synthetic fabrics are wrinkle-free and cheaper, and they dry more quickly. Synthetic pill coatings protect medicines and vitamins. Synthetic food containers and wraps keep foods fresh for a longer time.

Synthetic sporting surfaces such as artificial turf are easy to set up and maintain because they’re strong and durable. Many soccer fields and tennis courts have synthetic turfs. Synthetic materials have many benefits. Synthetic roofs are waterproof and durable. Synthetic shoes are lighter and cheaper than leather shoes. Vehicles with synthetic bodies are lighter and more fuel efficient than vehicles with steel bodies. Many household appliances, such as air conditioners and washing machines, are also made of synthetic materials.

Synthetic materials have made our lives easier. However, people are now concerned that synthetic materials, especially plastics, are harming our environment. Plastics are the most widely used synthetic material. Many items we use are made of plastic or contain plastic parts. Companies make more than 100 billion pounds of plastics each year.

People once thought that plastic’s ability to not wear out was a desirable property. However, once plastic items enter the waste stream, this property is no longer desirable. Because plastics don’t break down, they’re accumulating around us. Animals on land and in water mistakenly consume plastic, which harms them. In addition, some kinds of plastic release toxic chemicals into the environment.

Making and disposing of synthetic materials affects the amount of natural resources that are available. It also can harm the environment. These problems may not affect us in our lifetime. Who will these problems affect?

Human activities affect the environment. So, we need to consider the lives of future generations, not just our own. As we learned in the video, people who make and use products should consider how to sustain natural resources and how product disposal affects the environment. Being responsible will help preserve the environment for future generations.

Complete the following activity to compare the immediate impact and the future impact of a synthetic material. If we “look through the lens” of someone in the future, does that change our views on how we make and use synthetic materials today?

Beyond Cost and Performance

Can we have the benefits of synthetic materials and also preserve resources and the environment for future generations? The phrase “reduce, reuse, recycle” urges people to think about how to responsibly use and dispose of materials.

Reducing means to use fewer materials. One way to reduce is to buy products that use less packaging. Another way to reduce is to wait as long as possible to replace items. For example, people can wait until items are broken before replacing them.

Reusing is another way of decreasing the need for new products. Old clothes can be donated so that others can reuse them. Recycling is the process of converting waste materials into new products. Recycling helps protect the environment. It reduces the amount of resources and energy needed to make a product from scratch. For example, when paper is recycled, far fewer trees need to be cut down. We can buy new products that are made from recycled materials. For example, some notepads and paper boxes are recycled products. These items usually display a recycling symbol that lets people know the items were made from recycled materials. Recycling plastic is often more difficult than recycling other materials. In fact, some plastics can’t be recycled at all. For example, some milk jugs get remodeled into toys, but these toys often aren’t recyclable.

In the past, criteria for product design included only cost and performance. However, people now know that resources are limited and that some waste products, such as plastics, damage the environment. Many product manufacturers think about disposal during the design phase. Product criteria often include cost, performance, and impact on the environment. For example, the criteria for a new plastic food wrap could include the need for it to be biodegradable, which means that the plastic can be easily broken down by bacteria.

Everyone can do something to help protect our environment today and for future generations, while still having materials that meet our needs. Manufacturers can make safer materials. Consumers can reduce, reuse, and recycle. Cities and towns can make it easier to recycle.