Download Thermodynamics Practice

AP Chem
Thermodynamics Test
Each Problem = 5.5 points
1. The evaporation of a liquid is expected to have
A. Positive delta H and negative delta S
B. Negative delta H and negative delta S
C. Negative delta H and positive delta S
D. Positive delta H and positive delta S
E. These predictions cannot be made
2. The rxn 2C6H6 + O2 = 12CO2 + 6H2O
A. positive delta H and a negative delta S
B. negative delta H and a negative delta S
C. positive delta H and a positive delta S
D. negative delta H and a positive delta S
E. These predictions cannot be made
3.Given the following data, find the enthalpy change for this rxn.
2C + H2 = C2H2
C + O2 = CO2 delta H = -393.5 KJ
H2 + 1/2O2 = H2O(l) delta H = -285.8KJ
C2H2 + 5/2O2 = 2CO2 + H2O(l) delta H= -1299.8KJ
A.
B.
C.
D.
E.
454 KJ
–227 KJ
0 KJ
227 KJ
–454 KJ
4. Which of the following have a negative entropy change (delta S)
1. 2H2 + O2 = 2H2O(l)
2. 2NH3 = N2 + 3H2
3. Ca + Cl2 = CaCl2
A.
B.
C.
D.
E.
2 only
1 only
1,2, and 3
3 only
1 and 3
5. The energy required to convert a liquid to a gas is called the
A. Heat of fusion
B. Heat of boiling
C. Heat of vaporization
D. Free energy
E. Activation energy
6. A process in which the entropy of the universe increases is
A. spontaneous
B. exothermic
C. exoergic
D. endothermic
E. endoergic
7. When a solid sublimes to make a gas what are the respective signs for delta H and delta S?
A. +/+
B. -/C. +/D. -/+
E. Depends on the identity of the substance
8. An endothermic rxn can be spontaneous if
A. The products have more entropy than the reactants.
B. The reactants have more entropy than the products.
C. The reactants act as a cold sink.
D. The entropy of the surroundings increases.
E. None of the above
9. When a liquid freezes what are the values for delta H, S, and G?
A. +,-,0
B. -,+,0
C. -,-,0
D. +,+,0
E. +,+,+
F. -,-,10. What is the heat of formation of benzene (C6H6)if the heat of combustion is –3268KJ/mol. Assume the
water formed is liquid and use the data from problem 3.
A. 98KJ/mol
B. 49KJ/mol
C. –98KJ/mol
D. –49KJ/mol
E. None of these
11. Solid X is placed in contact with solid Y. Heat will flow spontaneously from X to Y when
A.
B.
C.
D.
E.
X is 20°C and Y is 20°C
X is 10°C and Y is 5°C
X is -25°C and Y is -10°C
X is 25°C and Y is 30°C
X is 25°C and Y is 25°C
12. Which physical changes are endothermic?
A. melting and freezing
B. melting and evaporating
C. condensation and sublimation
D. condensation and deposition
E. condensation and freezing
13. Which statement describes characteristics of an endothermic reaction?
A.
B.
C.
D.
E.
The sign of H is positive, and the products have less potential energy than the reactants.
The sign of H is positive, and the products have more potential energy than the reactants.
The sign of H is negative, and the products have less potential energy than the reactants.
The sign of H is negative, and the products have more potential energy than the reactants.
The sign of G is negative.
Base your answers to questions 14 through 15 on the potential energy diagram and the equation below.
2 C(s) + H2(g) + 227.4 kJ → C2H2(g)
14. The letter B represents which chemical formula or formulas in the equation?
15. If 682.2 kilojoules are absorbed, how many moles of C2H2(g) are produced?
16. C3H8 + 5O2 = 3CO2 + 4H2O(l)
deltaH = -1039.4KJ
A. Calculate the mass of propane burned when 3347.2 KJ of heat are reacted.
B. Calculate the amount of heat released when 65g of O2 are released.
17. Find delta H for the rxn: C6H12O6 = 2C2H5OH + 2CO2
The enthalpies of formation are:
C6H12O6 = -989.1 KJ
C2H5OH = -277.6 KJ
CO2 = -393.5 KJ
18. Find the delta H for the oxidation of ammonia: 4NH 3 + 3O2 = 2N2 + 6H2O(g)
1/2N2 + 3/2H2 = NH3
delta H = -46.2 KJ
H2 + 1/2O2 = H2O(l)
delta H = -285.8 KJ
H2 + 1/2O2 = H2O(g)
delta H = -241.8 KJ
19. Which is a superior fuel, propane or ammonia? Give 2 reasons why your choice is superior.
20. When 15g of CH3OH is burned in a calorimeter, the temperature increases by 8.3C. The specific heat
of water is 4.184J/gC and the calorimeter contains 5kg of water. The calorimeter constant is 3100J/gC.
What is the enthalpy change when one mole of methanol burns? Full credit: Ignore calorimeter. Extra
credit: Account for calorimeter
21. How much heat is absorbed when 10g of water boil?
22. How much heat is released when 10g of water freezes?
23. What is the final temperature when a 5g hunk of ice at -20C is added to 100 g of water at 80C?
Specific heat of ice = 2.1J/gC
24. What is the specific heat of aluminum if a 50g sample at 100C raises the temp of 100g of water at 25C
to 31.2C?
25. Where would the steam engine of a ship run the most efficiently, in the Arctic or in the tropics? Why?