Pre-AP Chemistry Homework Packet

Name______Period______

Pre-AP Chemistry Homework Packet Heat and Energy

Terms to Know:

Calorie calorie Calorimeter Chemical Potential Energy Energy Enthalpy Heat Joule Law of Conservation of Energy Specific Heat Spontaneous Process Surroundings System Temperature Thermometer Thermochemistry Universe

1 Calorie, calorie and Joule Problems

1. One serving of pretzels contains 115 Calories. How many calories does this equal?

2. A typical female should eat around 1200 Calories a day. How many joules of heat are expelled from this amount of Calories?

3. An exothermic reaction expels 86.5kJ of heat. How many calories does it release?

4. Two slices of cheese pizza contains 550 Calories. How many joules of energy does this equal?

5. A carrot puts out 176000 Joules of heat energy. How many Calories are in a carrot?

6. A reaction puts out 5.64x106 calories. How many Calories does this equal?

7. Just by resting, you are burning 78 Calories per hour. How many joules of heat energy is your body using?

8. When you run, your body consumes 5020000 Joules of heat energy per hour. How many Calories did your body burn?

2 Chemical Reactions That Involve Heat

On the line to the left, write the vocabulary word that best matches the definition given.

Heat Thermochemistry Exothermic Reaction Joule Endothermic Reaction Combustion

______1. Reactions that release heat

______2. The SI unit of heat and energy

______3. The energy that is transferred from one object to another

______4. The study of the changes in heat in chemical reactions

______5. Example of an exothermic reaction

______6. Reactions that absorb heat

If the statement is true, write TRUE. If the statement is FALSE, change the underlined word or phrase to make the statement true. Write your answer on the provided line.

______7. It is energy that maintains your body temperature close to 37°C.

______8. Bond breaking in chemical reactions release energy.

______9. Heat is transferred between two objects that are at the same temperature.

______10. An exothermic reaction absorbs heat from the environment.

______11. All combustion reactions are exothermic.

______12. If a reaction is endothermic, the amount of heat appears on the right side of the arrow in the balanced equation.

______13. Energy can be stored in the chemical bonds of a substance.

Answer the following questions in the space provided.

14. Provide two examples from daily life that demonstrate how heat is transferred from one object to another.

3 15. Why is the joule, the SI unit for energy, also the appropriate unit for measuring heat?

16. Provide an analogy that explains why bond breaking requires energy.

17. When ammonium chloride dissolves in a beaker of water, the beaker becomes cold to the touch. Explain why and how this happens.

If the statement is true, write TRUE. If the statement is FALSE, change the underlined word or phrase to make the statement true. Write your answer on the provided line.

______1. Energy is the ability to do work or produce heat.

______2. The law of conservation of energy states that energy can be created and destroyed.

______3. Chemical potential energy is the energy stored in a substance because of its composition.

______4. Heat is a form of energy that flows from a warmer object to a colder object.

______5. A calorie is the amount of energy required to raise the temperature of one gram of pure water one degree Celsius.

______6. A calorie is the SI unit of heat and energy.

______7. The specific heat of a substance is the amount of heat required to raise the temperature raise the temperature of one gram of that substance by one degree Celsius.

______8. Kinetic energy is the energy of motion.

______9. Chemicals participating in a chemical reaction contain only potential energy.

______10. One nutritional Calorie is equal to 100 calories.

______11. One calorie equals 4.184 joules.

4 ______12. When fuel is burned, some of its chemical potential energy is lost as heat. Specific Heat Problems

Specific Heat of Water =4.184 J/ g °C 1. A sample of mercury is heated from 25.5 °C to 52.5 °C. In the process, 3050J of heat are absorbed. What mass of mercury was in the sample? The specific heat of mercury is 0. 140 J/g °C.

2. A block of aluminum with a mass of 140g is cooled from 98.4oC to 62.2oC with a release of -1137J of heat. From this data, calculate the specific heat of aluminum.

3. A cube of gold with a mass of 192.4 g is heated from 30.0 oC to some higher temperature with the absorption of 921 J of heat. The specific heat of gold is 0.129 J/g oC. What is the final temperature of the gold?

4. A total of 226 J of heat are absorbed as 58.3 g of lead is heated from 12.0oC to 42.0oC. From this data, what is the specific heat of lead?

5. What is the change in heat energy when 114.32g of water at 14.85oC is raised to 18.00oC?

6. What is the change in heat energy when 132g of copper at 32.2°C is raised to 45.0oC? The specific heat of copper is 0.385 J/g °C.

7. What is the change in heat energy when 40.0g of water at 25.0oC is raised to 60.0oC?

5 8. If a 38g sample of water releases 621J of heat energy and cools to 4.00 0C. What was the initial temperature of the water?

9. What is the change in heat energy when 125g of water at 10.0oC is raised to 90. 0oC?

10. What is the change in heat energy when 64.82 g of aluminum metal at 100.0oC is cooled to 82.0 oC? The specific heat of aluminum is 0.897 J /g °C.

11. What is the final temperature if 24g of water at 50°C absorbs 985 J of heat energy?

12. What is the mass of a sample of iron if that sample lost -2300J of heat energy when it cooled from 80 oC to 30°C? The specific heat of iron is 0.449 J /g °C.

13. What is the specific heat of metal if its mass is 26.86g and it requires 418.6 J of heat energy to raise its temperature from 27.4 oC to 67.3°C?

14. If 41grams of water at 24°C absorbs 2208J of heat energy, what will be the final temperature of the water?

6 Using a Calorimeter

Use the calorimeter picture to answer the following questions.

1. The calorimeter shown in the picture is used to measure the caloric content of foods. To do this, the sample of food is burned inside the reaction chamber of the calorimeter. What is the system? What are the surroundings?

7 2. What besides food must be added to the chamber? Explain why. (Hint: think about what type of reaction is occurring and what reactants must be present)

3. What are the products of the reaction that takes places in the chamber?

4. Why is the calorimeter insulated?

5. What does the thermometer measure?

6. Describe the movement of heat as the reaction takes place inside the chamber.

7. Assuming that no heat escapes from the calorimeter, what equation would you use to determine the amount of heat released by the burning food in the reaction chamber? Define all variables in the equation.

8. Will the answer obtained from the equation in question 7 have a negative or positive value? Explain why.

8 Heat and Chemical Reactions

On the line to the left, write the vocabulary word that best matches the definition given.

System Calorimeter Thermochemistry Universe Enthalpy Enthalpy of Reaction Surroundings

______1. An insulated device used to measure the amount of heat absorbed or released during a chemical or physical process

______2. The study of heat changes that accompany chemical reactions and phase changes.

______3. The specific part of the universe that contains the reaction or process you wish to study.

______4. The change in enthalpy in a chemical reaction.

______5. A system plus its surroundings.

______6. The heat content of a system.

______7. Everything in the universe except the system being studied.

Fill in the blanks using the appropriate word or phrase from the list below.

Less Than Endothermic Change Moles Energy Exothermic Enthalpy Pressure

1. The heat absorbed or released in a reaction depends on the quantity called

______.

2. The enthalpy of a substance is almost exactly the same as the ______of a substance. 3. The symbol ∆H literally means a ______in enthalpy.

4. The ∆H for a(n) ______reaction always has a positive sign.

5. In an exothermic reaction, Hproducts will always be ______Hreactants.

6. Describe these as endothermic or exothermic processes: a. C2H5OH melts b. Water condensates 9 c. CH3OH vaporizes d. Ammonia freezes

Answer the following questions: 1. If you were only given ∆H for a reaction, could you determine if the reaction was endothermic or exothermic? Explain your answer.

2. Complete the following table: Sign of ∆H Reaction Heat Transfer Positive

Exothermic

3. Cheryl was asked to classify some chemical reactions as either endothermic or exothermic. She added 5.0g of five different solids to 20mL of water and monitored the temperature change until the entire solid had dissolved. The results of the experiment are shown in the table below.

Solid Beginning water Final water Change in water temperature temperature temperature

NH4NO3 25.4°C 22.1°C -3.3°C

CaCl2 25.4°C 28.9°C +3.5°C LiCl 25.4°C 23.9°C -1.5°C NaCl 25.4°C 25.1°C -0.3°C NaOH 25.4°C 29.5°C +4.1°C

a. List the compounds that underwent exothermic reactions in solution and those that underwent endothermic reactions.

b. How could you determine which solid releases the greatest amount of heat per mole?

+ - c. The equation for NaOH dissolving in water is NaOH(s)  Na + OH . Rewrite this equation to include the word “energy” in its appropriate location.

10 d. Explain what happens to the energy that “disappears” from the water in an endothermic reaction.

Heat in Chemical Reactions

For the following equations or phase changes, tell if it is endothermic or exothermic.

1. Deposition

2. Na3PO4 + KOH + heat  NaOH + K3PO4

3. MgF2 + Li2CO3  MgCO3 + LiF ∆H= -45.8kJ

4. Evaporation

5. Heat + P4 + O2  P2O3

6. RbNO3 + BeF2  Be(NO3)2 + RbF + heat

7. Melting

8. AgNO3 + Cu + energy  Cu(NO3)2 + Ag

9. CF4 + Br2  CBr4 + F2 ∆H= 65.77kJ

10. Changing from a liquid to a solid

11.HCN + CuSO4  Energy + H2SO4 + Cu(CN)2

12.Changing from a solid to a gas

13.GaF3 + Cs  CsF + Ga ∆H= -667.20kJ

14. Condensation

15.BaS + PtF2  BaF2 + PtS + Heat

11 Enthalpy Changes Problems

1. How much heat will be released when 6.44g of sulfur reacts with excess oxygen according to the following reaction?

S + O2 → SO3 ΔH= -791.4kJ

2. How much heat will be released when 4.72g of carbon reacts with excess oxygen according to the following equation?

C + O2 → CO2 ΔH= -393.5kJ

3. How much heat will be absorbed when 38.2g of bromine reacts with excess hydrogen according to the following equation?

H2 + Br2 → HBr ΔH=72.80kJ

4. How much heat will be released when 1.48g of chlorine reacts with excess phosphorous according to the following equation?

P + Cl2 → PCl5 ΔH=-886kJ

5. How much heat will be released when 4.77 g of ethanol reacts with excess oxygen according to the following equation?

C2H5OH + O2 → CO2 + H2O ΔH=-1366.7kJ

12 6. How much heat will be absorbed when 13.7g of nitrogen reacts with excess oxygen according to the following equation?

N2 + O2 → NO ΔH=180kJ

7. How much heat will be released when 11.8g of iron reacts with excess oxygen according to the following equation?

Fe + O2 → Fe3O4 ΔH=-1120.48kJ

8. How much heat will be released when 18.6g of hydrogen reacts with excess oxygen according to the following equation?

H2 + O2 → H2O ΔH=-571.6kJ

9. How much heat will be transferred when 14.9g of ammonia react with excess oxygen according to the following equation? Is this reaction endothermic or exothermic?

NH3 + O2 → NO + H2O ΔH=-1170kJ

10. How much heat will be transferred when 5.81g of graphite reacts with excess hydrogen according to the following equation? Is this reaction endothermic or exothermic?

C + H2 → C6H6 ΔH=49.03kJ

13 Additional Review Problems

1. Explain how energy changes from one form to another in an exothermic reaction. In an endothermic reaction.

2. Distinguish between kinetic and potential energy in the following examples: two separated magnets, an avalanche of snow, books on a library shelf, a mountain stream, a stock-car race, separation of charge in a battery.

3. Explain how the light and heat of a burning candle are related to chemical potential energy.

4. Describe how you would calculate the amount of heat absorbed or released by a substance when the temperature changes.

5. Explain why ∆H for an exothermic reaction always has a negative value.

6. Explain why you need to know the specific heat of a substance in order to calculate how much heat is gained or lost by the substance as a result of a temperature change.

7. Describe what the system means in thermodynamics, and explain how the system is related to the surroundings and the universe.

14 8. Write a complete thermochemical equation for the combustion of ethanol (C2H5OH). ∆H=-1367kJ/mol.

9. Determine which of the following are exothermic or endothermic: a. C2H5OH(l)  C2H5OH(g)

b. Br2(l)  Br2(s)

c. C5H12(g) + 8O2(g)  5CO2(g) + 6H2O(g)

d. NH3(g)  NH3(l)

e. NaCl(s)  NaCl(l)

10. Compare and contrast temperature and heat

11.How is the energy in gasoline converted and released when it burns in an automobile combustion reaction?

12. Ethanol is used as an additive in gasoline. The combustion of 1 mole of ethanol releases 1367kJ of energy. How many Calories are released?

13. To vaporize 2.00g of ammonia, 656 calories are required. How many kilojoules are required to vaporize the same mass of ammonia?

14. Why is a foam cup used in a student calorimeter rather than a typical glass beaker?

15 15. What is the sign for ∆H for an exothermic reaction? Endothermic reaction?

Answers to Math Problems

1. 1.15x105 cal 2. 5.0x106 J 3. 2.07x104 cal 4. 2.3x106 J 5. 42.1 Cal 6. 5640 Cal 7. 3.3x105 J 8. 1.20 x103 Cal

1. 807g 2. 0.22 J/g°C 3. 67.1°C 4. 0.129 J/g°C 5. 1510 J 6. 650.J 7. 5860J 8. 7.9°C 9. 41800J 10. -1050J 11. 60.°C 12. 1.0x102g 13. 0.391 J/g°C 14. 37°C

1. -79.5kJ 2. -155kJ 3. 17.4kJ 4. -3.70kJ 5. -141kJ 6. 88.0kJ 7. -78.9kJ 8. -2630kJ 9. -256kJ 10.3.95kJ