Chemical Reactions and Quantities Chapter 7
Chemical Reactions occur Everywhere… • …when fuel burns with oxygen in our cars to make the car move… • …when we cook our food… • …when we dye our hair… • …in our bodies, chemical reactions convert food into molecules that build and move muscle… • …in leaves of trees and plants, carbon dioxide and water are converted to carbohydrates… Some chemical reactions are simple, whereas others are quite complex… • However, they can all be written by chemical equations that chemists use to describe chemical reactions.
• In every chemical reaction, atoms are rearranged to give new substances. – Just like following a recipe, certain ingredients are combined (and often heated) to form something new.
Chapter Seven
7.1 – Equations for Chemical Reactions 7.2 – Types of Reactions 7.3 – Oxidation-Reduction Reactions 7.4 – The Mole 7.5 – Molar Mass and Calculations 7.6 – Mole Relationships in Chemical Equations 7.7 – Mass Calculations for Reactions 7.8 – Limiting Reactants and Percent Yield 7.9 – Energy in Chemical Reactions 7.1 Equations for Chemical Reactions
Write a balanced equation from formulas of the reactants and products for a reaction; determine the number of atoms in the reactants and products.
Chemical Change
• A chemical change occurs when a substance is converted into one or more new substances that have different formulas and properties.
• For example, when silver tarnishes, the shiny, silver metal (Ag) reacts with sulfur (S) to become the dull, black substance we call tarnish
(Ag2S). Chemical Reaction
• A chemical reaction always involves a chemical change because atoms of the reacting substances form new combinations with new properties.
• For example, a chemical reaction (and chemical change) takes place when a piece of iron (Fe) combines with oxygen (O2) in the air to produce a new substance, rust (Fe2O3), which has a reddish- brown color.
Evidence of a Chemical Reaction
During a chemical change, new properties are often visible, which indicates that a chemical reaction took place. Chemical Equation
When you build a model airplane or prepare a new recipe, you follow a set of direction.
These directions tell you what materials to use and the products you will obtain.
In chemistry, a chemical reaction tells us the materials we need and the products that will form.
Writing a chemical equation
Suppose you work in a bicycle shop assembling wheels and frames into bicycles.
You could represent this by a simple equation: Writing a chemical equation
Return to the silver example:
When silver tarnishes, the shiny, silver metal (Ag) reacts with sulfur (S) to become the dull, black substance we call tarnish (Ag2S).
* Unbalanced equation Writing a chemical equation
Return to the iron example: A chemical reaction takes place when a piece of iron (Fe) combines with oxygen (O2) in the air to produce a new substance, rust (Fe2O3), which has a reddish-brown color.
Generally, each formula is followed by an abbreviation, in parentheses, that gives the physical state of the substance. solid (s) liquid (l) gas (g) aqueous (aq) dissolved in water * Unbalanced equation Writing a chemical equation
Some reactions require heat to be added in order for the change to occur.
For example, when you burn charcoal in a grill, the carbon (C) in the charcoal combines with the oxygen (O2) to form carbon dioxide.
* Unbalanced equation Chemical equation symbols
Cu(s) + S(s) → CuS(s)