* AP Chemistry by Satellite Lectureguide
* Student Edition

Thermochemistry

Chapter 4

Objectives

Following your study of this chapter, you should be able to

- define the terms
*thermodynamics*and*thermochemistry*. - describe the kinetic and potential energy and calculate the amount of kinetic energy of a

moving object. - state the unit conversion relating joules and calories.
- describe the difference between temperature and heat, and between mechanical work

and heat. - distinguish between the system and the surrounding in a chemical process.
- define the terms
*exothermic*and*endothermic*as they apply to chemical reactions. - define the terms
*specific heat*and*heat capacity*and use both concepts to calculate heat

flow. - draw a coffee-cup calorimeter and label the important parts.
- calculate heat flow in a coffee-cup calorimetry experiment.
- draw a bomb calorimeter and label the important parts.
- calculate heat flow in a bomb calorimeter experiment.
- state the first law of thermodynamics.
- write the mathematical equation defining the internal energy change in a chemical

reaction. - calculate the internal energy change for a chemical process in terms of heat flow and

work. - write the mathematical equation for heat flow in chemical reactions at constant volume

and constant pressure. - define the term
*enthalpy*(H) and distinguish it from*internal energy*(E). - list the important characteristics of enthalpy of a chemical reaction.
- describe and recognize state functions.
- calculate the enthalpy change in a chemical reaction using Hess's Law.
- define the term
*standard state*as it is applied to an element or compound. - write a chemical equation describing the formation of any compound and look up its

heat of formation in table of standard heats of formation. - calculate the enthalpy change in any chemical reaction using standard enthalpies of

formation. - calculate the fuel value (heat of combustion) of a chemical compound using standard

1a. Describe the chemical and physical changes observed in the two reactions which were demonstrated in lecture. Indicate the energy change which occurred in each reaction.

b) Define the term *thermodynamics* and explain how the term *thermochemistry* is related to
thermodynamics.

2a. Distinguish between the meaning of the terms *kinetic energy* and *potential energy*.

3. What is the SI unit for energy? State the unit conversion factor relating the SI unit to calories.

4. Distinguish between the meaning of the terms *temperature* and *heat*. Provide an example of
two objects that are at the same temperature, yet contain different amounts of heat.

5. Identify the meaning of the terms *system* and *surroundings* for chemical reactions. Provide
an example distinguishing between system and surroundings.

6. Define the terms *exothermic* and *endothermic*. (Using a sketch similar to that used in
lecture, show how heat flows between system and surrounding for both types of process.)

7a. Distinguish between the meaning of the terms specific heat and heat capacity. What would
be the relative temperature change for two substances of equal mass, but having different
specific heats, upon absorbing an equal amount of heat?

8. Label the important components of the coffee-cup calorimeter shown below. What
property of a chemical reaction does a coffee-cup calorimeter measure? What type of
reactions are studied?

9a. Write the mathematical equation that relates the heat released by the chemical reaction to the heat absorbed by the water and the coffee-cup calorimeter.

10. Label the important components of a bomb calorimeter shown below. What property of a chemical reaction does a bomb calorimeter measure? What type of reaction is studied?

11a. Write the mathematical equation that relates the heat released by the chemical reaction to the heat absorbed by the water and the bomb calorimeter.

Problem Set #6

* AP Chemistry by Satellite*

ALL work must be shown to receive full credit.

PS6.1. Rank the following substances from lowest specific heat to highest specific heat.

C*(s)*, Fe*(s)*, N_{2}*(g)*, H_{2}O*(l)*, Hg*(l)*

PS6.2. Rank the following substances from lowest heat capacity to highest heat capacity.

1 kg H_{2}O*(l)*, 10 kg Cu*(s)* cube, 5 kg Fe*(s)* ball, 5 kg C*(s)* rod

PS6.3. Below is a table of specific heats for several different metals

Calculate the molar heat capacity
_{}
^{ for each of the metals. Based on the results}

of your calculations, estimate the specific heats of iron and silver.

PS6.4a. How much heat must be absorbed by a 75.0 g sample of water for the temperature to change from 24.5 ºC to 63.8 ºC?

b. Calculate the temperature change if a 75.0 g sample of zinc absorbed the same amount
of heat. The specific heat of zinc is listed in problem 6.3.

PS6.5. A 28.4 g sample of an unknown metal was heated to 110.0 ºC and plunged into a 100 g
sample of water initially at a temperature of 24.60 ºC. The final temperature of the
mixture was 25.34 ºC. Calculate the specific heat of the metal. Identify the metal.

PS6.6. When 1.000 g of KNO_{3} is dissolved in 120.0 g of water initially at 24.25 ºC in a
coffee-cup calorimeter, the final temperature is found to be 23.44 ºC. Calculate the heat
absorbed per gram and per mole when KNO_{3} dissolves in water. (Assume the heat
capacity of the calorimeter is zero.)

PS6.7. Calculate the heat produced per mole of aspirin when 2.216 g of C_{9}H_{8}O_{4} are reacted with
excess oxygen in a bomb calorimeter containing 4.40 kg of water. The temperature
change measured is 2.32 ºC. The heat capacity of the calorimeter is 2340 J/ ºC) .

12. State the first law of thermodynamics both in words and using a mathematical equation.

13a. What is the definition of the internal energy of a chemical system? Can the exact amount of
the internal energy be calculated for stable chemical systems? Can a change in internal
energy during a chemical reaction be calculated?

b) Given the chemical equation

And the diagram

14. Write the mathematical equation that relates the internal energy change to heat flow and work.

15a. Rewrite equation in Exercise 14 for the special case of a constant volume reaction (as in a
bomb calorimeter).

b) Rewrite equation in Exercise 14 for the special case of a constant pressure reaction (as in a
coffee-cup calorimeter).

16. Define *enthalpy* in terms of internal energy.

17a. List the three important properties which are important when using enthalpy.

18. Define the term *state function*.

19a. Define *Hess' Law*.

20. Define the term *standard state* as it is used in chemical thermodynamics.

21. Define the term *standard heat of formation* and provide several examples of chemical
equations that characterize a formation reaction.

22a. Define the term *heat of reaction* and write the mathematical equation used to calculate the
heat of a chemical reaction.

23. Define the term *fuel value* and list several compounds and their respective fuel value.

Problem Set #7

* AP Chemistry by Satellite*

ALL work must be shown to receive full credit.

is -683 kJ. Calculate the heat produced when 2.57 g of CaBr_{2} are formed.

PS7.3. For which of the following reactions is
_{}
reasoning in each case.

PS7.4. Given the enthalpy change for the two reactions

PS7.5. Given the following equations;

PS7.6. Using a table of Standard Enthalpies of Formation in your text or another reference
book, calculate the enthalpy of reaction for each of the following;

PS7.7. The molar heat of combustion of nitroethane, C_{2}H_{5}NO_{2}*(l)*, to CO_{2}*(g)*, H_{2}O*(l)* and N_{2}*(g)
* at 25 ºC is -1348 (kJ/mol). Determine the
_{}
for nitroethane.

PS7.8a. Given the following thermodynamic data,

Calculate _{}
for 1 mol of CaCl_{2}
dissolving in water. Is the dissolution of CaCl_{2}
endothermic or exothermic?

b. If 18.0 g of CaCl_{2} is added to 100. g of water initially at 23.5 ºC, calculate the
temperature of the solution after the CaCl_{2} dissolves. (Assume no heat is lost to the
container or the surroundings and the specific heat of the solution is the same as that of
water.)

PS7.8b. (Continued)

PS7.9. Determine the standard enthalpy of vaporization (transition from liquid to gas) for
CCl_{4}*(l)*.

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Diskette #3 Chemical Thermodynamics