AP Chem Ch. 5-6 Review Sheet
Gases & Thermochemistry
1. When aluminum foil is added to a solution of hydrochloric acid, the following reaction occurs:
2 Al(s) + 6 H+(aq) --> 2 Al3+(aq) + 3 H2 (g)
a.
b.
c.
d.
e.
f.
g.
h.
If 255 mL of H2 is produced, measured at 22°C and 740 mmHg, what is the yield of hydrogen in moles? In
grams?
What pressure would be required to compress the samle of H2 referred to in (a) to one-half of its volume at
22°C? At what temperature would the volume be doubled, if the pressure is held constant at 740 mmHg?
What is the density of H2 (g) at 22°C and 740 mmHg?
Suppose the hydrogen is collected over water at 25°C and a total pressure of 756 mmHg. What is the partial
pressure of H2 (g)? If the volume of the sample is 235 mL, what is the mass of H2?
What is the mole fraction of hydrogen in the wet gas in (d)?
What mass of aluminum is required to generate 1.00 L of H2 (g) at 25°C and 1.00 atm?
What volume of H2 at STP could be generated from 250 mL of "dilute" hydrochloric acid, in which the
molarity of the H+ is 6.0 mol/L?
Compare the rate of effusion of H2 to that of He; compare the time required for equal numbers of moles of H2
and CO2 to effuse.
2. Consider the thermochemical equation:
C2H6 (g) + 7/2 O2 (g) --> 2 CO2 (g) + 3 H2O (l); H = - 1559.7 kJ
Calculate H for the thermochemical equations:
2 C2H6 (g) + 7 O2 (g) --> 4 CO2 (g) + 6 H2O (l)
2 CO2 (g) + 3 H2O (l) --> C2H6 (g) + 7/2 O2 (g)
b. The heat of vaporization of H2O (l) is + 44.0 kJ/mol. Calculate H for the equation:
C2H6 (g) + 7/2 O2 (g) --> 2 CO2 (g) + 3 H2O (g)
c. The heats of formation of CO2 (g) and H2O (l) are -393.5 and -285.8 kJ/mol, respectively. Calculate Hf of 2
C2H6 (g).
d. How much heat is evolved when 1.00 g of 2 C2H6 (g) is burned to give CO2 (g) and H2O (l) in an open
container?
e. When 1.00 g of 2 C2H6 (g) is burned in a bomb calorimeter, the temperature rises from 22.00°C to 33.13°C. In
a separate experiment, it is found that absorption of 10.0 kJ of heat raises the temperature of the calorimeter by
2.15°C. Calculate Ccalorimeter and qreaction.
f. Calculate E at 25°C for the equation:
C2H6 (g) + 7/2 O2 (g) --> 2 CO2 (g) + 3 H2O (l)
a.
ANSWERS:
1.
a. 0.0103 mol; 0.0207 g
b. 1480 mmHg; 317°C
c. 0.0810 g/L
d. 732 mmHg; 0.0187 g
e. 0.968
f. 0.735 g
g. 17 L
h. 1.41; 0.214
2.
a.
b.
c.
d.
e.
f.
-3119.4 kJ; + 1559.7 kJ
-1427.7 kJ
-84.7 kJ
51.9 kJ
4.65 kJ/°C, -51.8 kJ
-1553.5 kJ