Thermochemistry Test Review: Multiple Choice Problems
1. What is the correct order, from highest to lowest molar heat value, for the three types of energy change?
a. Chemical, phase, nuclear c. Nuclear, phase, chemical
b. Phase, chemical, nuclear d. Nuclear, chemical, phase
2. Which metal requires the most energy to raise 1.00 g of it by 1.00ºC? (Refer to Chemistry Data Booklet.)
a. Aluminum b. Copper c. Lead d. Nickel
3. What is the specific heat capacity of a substance if 2.41x104 J are needed to change the temperature of 105.0 g of it from 25.0ºC to 250.0ºC?
a. 1.02 x 10-4 J/gºC b. 9.18 x 10-4 J/gºC c. 0.918 J/gºC d. 1.02 J/gºC
4. Which statement about enthalpy is true?
a. Heat is given off to the surroundings in endothermic reactions.
b. Some substances have a negative specific heat capacity.
c. Specific heat capacity is the same for all liquids.
d. The sign of ∆H is always negative in exothermic reactions.
5. What happens to the value of ∆H for a thermochemical reaction if the reaction is reversed?
a. ∆H has the same numerical value, and the sign changes.
b. ∆H has the same numerical value, and the sign remains the same.
c. ∆H is the reciprocal of the original value, and the sign changes.
d. ∆H is the reciprocal of the original value, and the sign remains the same.
6. Which is an exothermic process?
a. Ice melting c. Water evaporating
b. Water boiling d. Water vapour condensing
7. Which statement is true for the combustion of ethanol?
C2H5OH (l) + 3O2(g) → 2CO2 (g) + 3H2O(l) ∆H = -1370 kJ
a. The enthalpy change would be the same is gaseous water were produced.
b. The potential energy of the products is less than the potential energy of the reactants.
c. The products of the reaction occupy a larger volume than the reactants.
d. The reaction is endothermic.
8. What is the energy required to evaporate two moles of liquid water given the following equations?
2H2(g) + O2(g) → 2H2O(g) ∆H = -483.6 kJ
2H2(g) + O2(g) → 2H2O(l) ∆H = -571.6 kJ
a. 44.0 kJ b. 88.0 kJ c. 527.6 kJ d. 1055.2 kJ
9. Which statement correctly describes an endothermic chemical reaction?
a. The products have higher potential energy than the reactants, and the ∆H is negative.
b. The products have higher potential energy than the reactants, and the ∆H is positive.
c. The products have lower potential energy than the reactants, and the ∆H is negative.
d. The products have lower potential energy than the reactants, and the ∆H is positive.
10. Given the thermochemical equation:
2NO2 (g) → 2NO(g) + O2(g) ∆H = 114 kJ
what is the ∆H for the reaction NO(g) + ½ O2(g) → NO2(g) ?
a. -114 kJ b. -57 kJ c. +57 kJ d. +114 kJ
11. Using the data below, what is the order of changes that occur when ethanol is heated from -25.0ºC to 85.0ºC?
Boiling point of ethanol: 78.5ºC
Melting point of ethanol: -117.3ºC
a. Phase change, temperature change
b. Phase change, temperature change, phase change
c. Temperature change, phase change
d. Temperature change, phase change, temperature change
12. Which statement best describes the formation of methanol, CH3OH(l), from the elements? (Refer to Data Booklet, page 5.)
a. It is endothermic and heat is absorbed.
b. It is exothermic and heat is released.
c. It is exothermic and heat is absorbed.
d. It is exothermic and heat is released.
13. Which process results in the greatest endothermic change for 10.0g of H2O?
a. Condensation
b. Melting
c. Solidification
d. Vaporization
14. The following decomposition reaction may occur in an air bag.
2NaN3(s) → 3N2 (g) + 2Na(s) ∆H = -43.5 kJ
What is the heat of formation, ∆Hf, for NaN3?
a. -43.5 kJ b. -21.8 kJ c. 21.8 kJ d. 43.5 kJ
15. A small sample released 2.0 x 1010 kJ of energy while undergoing a change. What type of change most likely occurred?
a. Chemical b. molecular c. nuclear d. physical
16. Given the following two reactions:
C(s) + O2(g) → CO2(g) ∆H = -393.5 kJ
2Fe(s) + 3/2 O2 (g) → Fe2O3(s) ∆H = -824.2 kJ
Calculate the enthalpy change for 2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)
a. -467.9 kJ b. -430.7 kJ c. 430.7 kJ d. 467.9 kJ
17. A substance increases in temperature by 255ºC when a 983 g sample of it absorbs 83 200 J of heat. What is the specific heat capacity of the substance?
a. 0.332 J/gºC b. 0.450 J/gºC c. 21.6 J/gºC d. 321 J/gºC
18. What is the ∆H value for an exothermic energy change?
a. Always negative
b. Always positive
c. Could be positive or negative
d. Depends on the potential energy of the reactants
19. How much heat is required to vapourize 15.8 g CH3OH(l) at its boiling point? (∆Hvap = 38.0 kJ/mol)
a. 2.41 kJ b. 18.8 kJ c. 77.0 kJ d. 600. kJ
20. What is the ∆H for the following reaction (Refer to the Data Booklet, page 5.)
2NO(g) + O2(g) ↔ 2NO2(g)
a. -114.0 kJ b. -28.5 kJ c. +57.0 kJ d. +778.0 kJ
21. Which of the following statements is true?
a. In an endothermic process heat is transferred from the surroundings to the system.
b. In an exothermic process heat is transferred from the surroundings to the system.
c. The surroundings will feel cooler in an exothermic process.
d. The surroundings will feel warmer in an endothermic process.
22. The enthalpy change for the following reaction is -184.6 kJ.
H2(g) + Cl2(g) → 2HCl(g)
What is the standard enthalpy of formation, ∆Hf, for HCl(g)?
a. -369.2 kJ b. -184.6 kJ c. -92.3 kJ d. +92.3 kJ
23. Calculate the ∆H for the following reaction using the bond energies given below:
H-H (g) + I-I (g) → 2H-I (g)
Bond energies: H-H = 436 kJ/mol, I-I = 151 kJ/mol, H-I = 297 kJ/mol
a. +290 kJ b. -290 kJ c. +7 kJ d. -7 kJ
24. Which of the following processes is exothermic?
a. Ether evaporating
b. Ice melting
c. Steam condensing
d. Water decomposing
25. Which process involves the largest difference in heat content between reactants and products?
a. H2(g) → H2(l) + heat
b. H2(g) → H2(s) + heat
c. H2(l) + heat → H2(g)
d. H2(l) → H2(s) + heat
26. What quantity of heat is evolved with 5.550 mol H2O(l) is formed from the combustion of H2(g) and O2(g)?
H2(g) + ½ O2(g) → H2O(l) ∆H = -285.8 kJ
a. 51.44 kJ b. 285.8 kJ c. 1586 kJ d. 2297 kJ
27. As energy is added to a substance, the temperature remains constant. How may the substance be changing?
a. From a gas to a solid
b. From a liquid to a gas
c. From a liquid to a solid
d. In the amount of kinetic energy
28. The addition of 9.54 kJ of heat is required to raise the temperature of 225.0 g of a liquid hydrocarbon from 20.5ºC to 45.0ºC. What is the heat capacity of this hydrocarbon?
a. 0.94 J/gºC b. 1.73 J/gºC c. 1.88 J/gºC d. 9.42 J/gºC
Answers:
1d 2a 3d 4d 5a 6d 7b 8b 9b 10b 11d 12d 13d 14c 15c
16d 17a 18a 19b 20a 21a 22c 23d 24c 25b 26c 27b 28b 29d 30d