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A.P. Chemistry Practice Test: Unit 4
Chapter 5: Thermochemistry

Multiple Choice.
1. The sketch below represents a cooling curve for water at 1 atm pressure. (Note: CI = heat capacity of water in region I, T = change in temperature between points specified, Hfus = heat of fusion.)

Which of the following statements is/are true?
I. No heat energy is being added or removed from the system between points B and C
II. The quantity of heat being removed from the system between points C and D is equal to CIII x m x t(C and D)
III. The quantity of heat being added to the system between points C and D is equal to CIII x m x t(C and D)
IV. The quantity of heat change in region I is equal to that of region III
V. Water is in the process of freezing in region II.
VI. Liquid water is in the process of cooling down in region III.

A. I, II, V B. II, V C. III, IV D. II, IV, V E. none of the above combinations

2. As a solid, a particular element has a heat capacity of 0.19 J/goC. When 3600 J of energy of heat is added to 18.0 g of the element initially at 0oC, it is still a solid. Its melting point is at least A. over 100oC B. over 500oC C. over 1000oC D. over 1500oC E. over 2000oC

3. Two 50 mL solutions of different ionic compounds are combined in a coffee cup calorimeter. The solutions go from 28.5oC to 21.9oC. Therefore, it can be concluded that the reaction between the two compounds A. is exothermic B. is endothermic C. has H > 0 D. both a and c are correct E. both b and c are correct

4. Calculate the heat of vaporization of carbon tetrachloride given that the standard molar enthalpy of formation of liquid carbon tetrachloride is -135.4 kJ/mol and the standard molar enthalpy of formation of gaseous carbon tetrachloride is -102.9 kJ/mol. A. +102.9 kJ/mol B. -32.5 kJ/mol C. +238.2 kJ/mol D. +32.5 kJ/mol E. -238.2 kJ/mol

5. The complete combustion of 1 mole of propane (C3H8) results in the liberation of 488.7 kcal. What is the heat of formation of propane given that the Hfo of CO2 (g) is -94.1 kcal/mol and that the has Hfo of H2O (l) is -57.8 kcal/mol. A. +6.9 kcal/mol B. -19 kcal/mol C. -24.8 kcal/mol D. -63.6 kcal/mol E. -1002.2 kcal/mol

6. Given the heats of the following reactions I. P4(s) + 6Cl2(g) 4PCl3(g) = -1225.6 kJ
II. P4(s) + 5O2(g) P4O10(s) = -2967.3 kJ
III. PCl3(g) + Cl2(g) PCl5(g) = -84.2 kJ IV. PCl3(g) + ½O2(g) Cl3PO(g) = -285.7 kJ

Calculate the value of for the reaction below: P4O10(s) + 6PCl5(g) 10Cl3PO(g)

a. -110.5 kJ b. -610.1 kJ c. -2682.2 kJ
d. -7555.0 kJ
e. -1620.5 kJ

7. Which of the following does NOT have a standard enthalpy of formation equal to zero at 25oC and 1.0 atm? A. F2 (g) B. Al (s) C. H2O (l) D. H2 (g) E. They all have standard enthalpies of formation equal to zero.

8. For which of the processes below would one expect the enthalpy of reaction to be negative? I. The temperature increases when calcium chloride dissolves in water. II. Steam condenses to liquid water. III. Water freezes. IV. Dry Ice Sublimes

A. IV only B. I, II, and III C. I only D. II and III only E. I and II only

9. For the combustion of ethyl alcohol, which of the following is (are) true? C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l) H = -1.37 x 103 kJ
I. The reaction is exothermic.
II. The enthalpy change would be different if gaseous water was produced.
III. The reaction is not an oxidation-reduction reaction.
IV. The initial temperatures of the products affects the enthalpy change for the reactants.

a. I, II
b. I, II, III c. I, III, IV d. III, IV e. I, II, IV

10. Consider the above reaction. When a 15.1 g sample of ethyl alcohol (C2H5OH) (molar mass = 46.1 g/mol) is burned, how much energy is released as heat? A. 0.449 kJ B. 2.25 x 103 kJ C. 4.49 x 102 kJ D. 1.02 x 103 kJ E. 196 kJ

11. Consider the reaction: H2 (g) + 1/2 O2 (g) --> H2O (l) H = -286 kJ
Which of the following are true? A. The enthalpy change for this reaction is the same as the enthalpy of formation of liquid water. B. The reaction is endothermic. C. The enthalpy of the products is higher than that of the reactants. D. b and c are true E. a, b, and c are true

12. Given the following two reactions at 298 K and 1atm, which of the statements is true? 1. N2(g) + O2(g) 2NO(g) H1 2. NO(g) + ½O2(g) NO2(g) H2

a. for NO2(g) = H2 b. for NO(g) = H1 c. H1 = H2 d. for NO2(g) = H2 + ½H1 e. two of these are true

13. The standard heat of formation of gaseous sulfur trioxide is -396 kJ/mol. What is the enthalpy of reaction represented by the following balanced equation? 2 SO3 (g)  2 S (s) + 3 O2 (g)

A. -396 kJ/mol
B. + 396 kJ/mol C. + 792 kJ D. – 792 kJ E. + 198 kJ

14. The potential energy of the reactants in an exothermic reaction is A. lower than the potential energy of the products B. the same as the potential energy of the products C. higher than the potential energy of the products D. not enough information is given

15. Given a large piece of copper and a small piece of copper, one can state that A. the heat capacity of both is the same B. the specific heat of both is the same C. both A and B D. neither A nor B

16. Water is a unique substance in that has quite a high specific heat, a high heat of fusion, and a high heat of vaporization. This means that when A. ice melts, a large amount of energy is absorbed from the surroundings B. sweat evaporates, a large amount of energy is removed from your body C. a large pool of water takes a long time to heat up to the same temperature as the air in summer D. the ocean is warmer than the air on most winter days E. all of the above

Problems. Show all work. ALL NUMBERS MUST HAVE UNITS! Answers must be reported to the correct number of sig figs.
17. Consider the reaction

What is the final temperature of the solutions when 100.0 mL of 0.50 M HCl at 24.0oC is reacted with 300.0 mL of 0.050 M Ba(OH)2 also at 24.0oC?

18. A 38.6 g piece of iron (specific heat = 0.45 J/g °C) was heated to 86.4°C and added to 115.0 g of water at 22.5°C in a coffee-cup calorimeter. Find the temperature when thermal equilibrium is reached. (Assume that all heat transfer occurs between the water and the metal.)

19. Calculate for the reaction

A 15.0 g chunk of sodium is dropped into 0.75 L of water at 22.5°C. What is the final temperature of the water after the above reaction occurs? Assume that all of the heat is used in raising the temperature of the water. (Hf values: Na (s) = 0, H2O (l), NaOH (aq) = -470 kJ, H2 = 0)

20. A 50.0 g sample of steam at 255.0°C cools down to ice at -79oC. How much heat was lost? (Sp. Heat of ice is 2.03 J/g °C, Sp. Heat of water is 4.184 J/g °C, Sp. Heat of steam is 2.10 J/g °C, the heat of vaporization of water 40.7 kJ/mole, the heat of fusion of water is 6.02 kJ/mole) Draw a cooling curve diagram to show what happens in this problem.

21. A. Write the reaction for which the enthalpy of reaction is the same as the enthalpy of formation of glucose, C6H12O6.

B. Given that the heat of formation of glucose is -1275 kJ/ mol, what is the enthalpy of the reaction above?

C. Would the reaction in which glucose is created in photosynthesis have the same enthalpy value?

D. How grams of glucose must have been in made in the reaction in A (above) if 212.5 J were released?

Key:
1. B 2. C 3. E 4. D 5. C 6. B 7. C 8. B 9. E 10. C 11. A 12. D 13. C
14. C 15. B 16. E

17. 25.1oC

18. 24.7oC

19. 70.00C

20. 175 kJ

21. A. 6 C (graphite) + 6 H2 (g) + 3 O2 (g)  C6H12O6 (s)

B. -1275 kJ

C. no D.