AP Chemistry Name ______
Period ___ Date ___/___/___
6 · Energy and Chemical Reactions
STUDY QUESTIONS
3. If the temperature of a 50.0-gram block of aluminum increases by 10.9 K when heated by 500 Joules, calculate the
a. heat capacity of the aluminum block
c. specific heat of aluminum
5. Calculate the heat necessary to change the temperature of one kg of iron from 25°C to 1000°C. The specific heat of iron is 0.451 JK-1g-1.
6. If a 40 gram block of copper at 100°C is added to 100 grams of water at 25°C, calculate the final temperature assuming no heat is lost to the surroundings. The specific heat of copper is 0.385 JK-1g-1 and the specific heat of water is 4.184 JK-1g-1.
7. Calculate the amount of heat needed to melt 27.0 g of ice if the heat of fusion of ice is 6.009 kJ/mol.
8. If 27.0 grams of ice at 0°C is added to 123 grams of water at 100°C in an insulated container, calculate the final temperature. Assume that the specific heat of water is 4.184 JK-1g-1.
9. A 50 gram block of an unknown metal alloy at 100°C is dropped into an insulated flask containing approximately 200 grams of ice. It was determined that 10.5 grams of the ice melted. What is the specific heat capacity of the unknown alloy?
10. If the enthalpy change for the combustion of propane is –2220 kJ/mole propane, what quantity of heat is released when 1 kg of propane is burned?
C3H8(g) + 5O2(g) ® 3CO2(g) + 4H2O(l) DH-2220 kJ
11. Using the following thermochemical data, calculate the molar heat of combustion, DH°combustion of methane, CH4:
2CH4(g) + 3O2(g) ® 2CO(g) + 4H2O(l) DH° = -1215 kJ
2C(s) + O2(g) ® 2CO(g) DH° = -221 kJ
C(s) + O2(g) ® CO2(g) DH° = -394 kJ
12. Calculate the standard molar enthalpy of formation of methane from the data given in question 11, your answer to question 11, and the following: DH°f (H2O(l)) = -286 kJ/mol
13. When ammonia is oxidized to nitrogen dioxide and water, the quantity of heat released equals 349 kJ per mol of ammonia:
2NH3(g) + 7/2O2(g) ® 2NO2(g) + 3H2O(l) DH° = -698 kJ
Calculate the standard molar enthalpy of formation of ammonia if
DH°f (H2O(l)) = -286 kJ/mol
DH°f (NO2(g)) = +33 kJ/mol
15. When 40 grams of ammonium nitrate is dissolved in 100 grams of water in a constant-pressure coffee-cup calorimeter, the temperature of the solution drops by 22.4°C. If the specific heat of the solution is 4.18 JK-1g-1, calculate the enthalpy of solution of ammonium nitrate.
AP Chemistry Name ______
Period ___ Date ___/___/___
17 · Entropy & Free Energy
STUDY QUESTIONS
1. Imagine tossing two coins in the air.
a. Predict the distribution of various combinations of heads and tails.
b. What is the probability of the result being two heads?
c. What is the most probable result?
Now imaging tossing three coins in the air.
d. What is the probability of a three heads result?
e. Which system has the highest entropy, the two-coin system or the three-coin system?
2. Which one of the following pairs of samples has the higher entropy?
a. Br2(l) or Br2(g)
b. C2H6(g) or C3H8(g)
c. MgO(s) or NaCl(s)
d. KOH(s) or KOH(aq)
3. Predict the entropy change for the following processes:
a. O2(g) ® 2O(g)
b. 2O3(g) ® 3O2(g)
c. CH4(g) + 2O2(g) ® CO2(g) + 2H2O(g)
d. NaCl(s) ® Na+(aq) + Cl-(aq)
e. C2H5OH(l) ® C2H5OH(g)
f. Ag+(aq) + Cl-(aq) ® AgCl(s)
9. Of the following reactions,
which are spontaneous at any temperature,
which are never spontaneous regardless of the temperature,
which are spontaneous only at a high temperature,
and which are spontaneous only at low temperature?
DH / DSa. / C8H18(l) + 25/2O2(g) ® 8CO2(g) + 9H2O(g) / - / +
b. / N2(g) + 2F2(g) ® N2F4(g) / - / -
c. / Cl2(g) ® 2Cl(g) / + / +
d. / 2O3(g) ® 3O2(g) / - / +
e. / 2C(s) + 2H2(g) ® C2H4(g) / + / -