CHEM 1A  Lecture Quiz 4 • Spring 2014
1.
Write whether each quantity below is POSITIVE (+), NEGATIVE (-) or ZERO (0) for the ADIABATIC
EXPANSION of an ideal gas.
q = ________ w = ________
2.
Name:_________________________________________
ΔV = ________
ΔE = ________
ΔT = ________
In the operation of a refrigerator, which step is endothermic, absorbing heat from inside the
refrigerator?
A. Adiabatic compression
B. Isothermal expansion
C. Adiabatic expansion
D. Isothermal expansion
E. None of above.
Please refer to the graph to the right for the next two
questions.
3.
Which transition would correspond to an
ISOTHERMAL compression?
A. 3 → 1
B. 1 → 2
C. 4 → 3
D. 2 → 4
E. 3 → 4
4.
Which transition would correspond to an
ADIABATIC expansion?
A. 1 → 3
B. 2 → 1
C. 3 → 4
D. 4 → 2
E. 3 → 1
5.
Circle ALL of the reactions below that are EXOTHERMIC:
A. CO2(s) → CO2(g)
B. PCl3(g) → PCl3(l)
C. H2O(l) → H2O(s)
D. C8H20(l) + 9 O2(g) → 8 CO2(g) + 10 H2O(g)
E. 6 CO2(g) + 6 H2O(l) → C6H12O6(s) + 6 O2(g)
6.
Consider the EXOTHERMIC reaction below:
PCl3 + Cl2 → PCl5
ΔH = -87.9 kJ
Based only on the information above, what can be concluded about the bond strengths of P & Cl?
A. a single Cl—Cl bond must be stronger than a single P—Cl bond
B. a single P—Cl bond must be stronger than a single Cl—Cl bond
C. a single P—Cl bond must be weaker than two Cl—Cl bonds
D. a single Cl—Cl bond must be weaker than two P—Cl bonds
E. None of the above.
7.
Using the table of average bond dissociation energies on the back page, calculate the change in
enthalpy (ΔHreaction) for the reaction below.
H—C≡C—H + 2 H2 → H3CCH3
ΔHreaction = ________________
8.
Certain parts of the world, such as southern California & Saudi Arabia, are short on freshwater for
drinking. One possible solution to the problem is to tow icebergs from Antarctica and then melt them as
needed. How much energy (in kJ) would be required to melt a moderately large iceberg with a mass of
1.00 million metric tons (1.00 x 106 tons)?
H2O(s) → H2O(l) ΔH = +6.01 kJ/mol
HINT: 1 metric ton = 1000. kg
9.
How much energy would be required to produce 10.0 moles of gaseous phosphorus atoms according to
the equation below?
P4(s) → 4 P(g)
ΔHreaction = +1258 kJ
10.
A cold block of iron metal (mass = 41.82 g, Cp = 0.450 J/g·oC) at -79 oC is placed in a calorimeter
containing 125 g of water at 25 oC. Assuming heat is only transferred from the warm water to the cold
metal, what is the final temperature of the system at thermal equilibrium?
11.
Consider the heat of vaporization data below:
Reaction 1:
H2O(l) → H2O(g)
ΔHvaporization = +44 kJ
Reaction 2:
C4H10(l) → C4H10(g)
ΔHvaporization = + 22 kJ
A. Based on the information above, CIRCLE the reaction below that would release the MOST heat.
Reaction 3:
2 C4H10(l) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
Reaction 4:
2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
Reaction 5:
2 C4H10(l) + 13 O2(g) → 8 CO2(g) + 10 H2O(l)
B. EXPLAIN your answer to part A. (above) by drawing an Enthalpy Diagram that includes Reactions 1-5.
12.
Using the reactions and data below, calculate the reaction enthalpy (ΔH°rxn) for the synthesis of
aluminum chloride. Show your work for full credit.
2 Al(s) + 3 Cl2(g) → 2 AlCl3(s)
ΔH°rxn = ______________
Hint: Pay close attention to the phases of each compound.
2 Al(s) + 6 HCl(aq) → 2 AlCl3(aq) + 3 H2(g)
ΔH° = −1049 kJ
HCl(g) → HCl(aq)
ΔH° = −74.8 kJ
H2(g) + Cl2(g) → 2 HCl(g)
ΔH° = −185 kJ
AlCl3(s) → AlCl3(aq)
ΔH° = −323 kJ
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EXTRA CREDIT: (5 points)
Instant hot and cold packs are often used by athletes to conveniently treat injury. They work by taking
advantage of ionic compounds that either absorb or release a lot of heat when dissolved in water. The water
and ionic compound are kept in separate compartments in the pack until needed; then the chambers are
broken and the ionic compound dissolves in the water, thereby absorbing or releasing heat to treat the injury.
Suppose a cold pack contains 500. grams of water. Given the molar enthalpy of dissolution of ammonium
nitrate (below), what is the minimum number of grams of NH4NO3(s) required to lower the temperature of the
cold pack from 22 oC to 0oC?
NH4NO3(s) → NH4+(aq) + NO3- (aq)
ΔHdissolution = +25.7 KJ/mol
Q=mCpΔT
where ΔT=(Tfinal-Tinitial), m = mass, and Cp = specific heat capacity
Specific Heat Capacity of H2O(l) = 4.184 J/g·oC