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Chemistry 40S
Thermodynamics Test
Not all questions are graded equally
MULTIPLE CHOICE: Circle the best possible answer
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Which statement is INCORRECT?
a) A process that absorbs energy from its surroundings is called endothermic.
b) In an exothermic reaction the enthalpy of species increases.
c) Energy is the capacity to do work or to transfer heat.
d) Kinetic energy is the energy of motion.
There are two properties of a reacting system that determine whether a process at constant pressure and
temperature can occur spontaneously. These are:
a) kinetic and potential energy change
b) heat and work
c) energy change and enthalpy change
d) enthalpy change and entropy change
Which process is accompanied by a decrease in entropy of the materials?
a) expansion of a gas into a vacuum
b) solution formation
c) crystal formation
d) diffusion of solute molecules into a region of low solute concentration
If for a reaction the H  0 and S  0 then the reaction is
a) probable at low temperature
b) probable at high temperature
c) probable no exceptions
d) improbable no exceptions
Consider the reaction below:
Fe2O3(s) + 2 Al(s) Al2O3(s) + 2 Fe(l)
a) The thermodynamic driving force for this reaction is the high stability (low free energy) of the Al 2O3.
b) This reaction is non-spontaneous
c) Fe3+ has a greater affinity for oxygen than Al3+
d) In this reaction S  0
A silver coin (54 g, 0.50 mol) with a specific heat of 0.235 J oC-1 g-1. at 90 oC is dropped into water (54 g, 3.0
mol) at 20.0 oC. What is the final temperature?
a) 25.31 oC
b) 24.78 oC
c) 24.25 oC
d) 23.72 oC
How much heat energy is required to warm 2 kg iron (roughly, a large cast iron skillet) from 20 C to 140 C?
The molar heat capacity of iron is 25.10 J mol-1 K-1.
a) +31,500 J
b) +64,300 J
c) -107.9 J
d) +107,900 J
From the following data at 25°C:
H2(g) + Cl2  2 HCl(g);
H° = -185 kJ
2 H2(g) + O2(g)  2 H2O(g);
H° = -483.7 kJ
Calculate H° at 25°C for the reaction below:
4 HCl(g) + O2(g)  2 Cl2(g) + 2 H2O(g)
a) +114 kJ
b) +299 kJ
c) -299 kJ
d) -114 kJ
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9.
Based on bond energies, what is the change in energy for the complete combustion of 1 mole of methanol,
CH3OH, into carbon dioxide and water?
BE(H-C) = 415 kJ/mol
BE(H-O) = 460 kJ/mol
BE(C=O) = 805 kJ/mol
a) -2,130 kJ/mol
b) -644 kJ/mol
c) -702 kJ/mol
d) -401 kJ/mol
BE(O=O) = 494 kJ/mol
BE(C-O) = 360 kJ/mol
10. At what temperature does the reaction below just become non spontaneous? Given: H = -176 kJ and
S = -284.5 J/K
NH3(g) + HCl(g)  NH4Cl(s)
a) 582 K
b) Just below 619 K
c) Just above 619 K
d) 680 K
11. Calculate the change in enthalpy per mole for the combustion of formaldehyde, CH2O. The reaction is:
CH2O(g) + __ O2(g)  __ CO2(g) + __ H2O(liq)
Data: A constant volume calorimeter has a heat capacity, Ccal, of 9.00 kJ/C. Burning 3.50 g formaldehyde
(0.11656 mol) causes the temperature of the calorimeter to go from 20.00 oC to 27.39 oC.
a) -605 kJ/mol
b) -571 kJ/mol
c) -1,041 kJ/mol
d) -890 kJ/mol
12. How much ice, in grams, is needed to cool a drink, say 355 mL of Diet Coke, from an initial temperature of 37
C (body temperature) to 5 C? Assume that the Diet Coke is water, and ignore the heat capacity of the very light
(about 15 g) aluminum can. The density of water is 1.0 g/mL.
Data: Cp(water) = 75.3 J mol -1 K-1; DHfus(water) = 6,010 J mol -1 (fusion = ice melting)
a) 111 g
b) 91 g
c) 51 g
d) 142 g
13. A hot pack contains 100 g (0.8309 mol) of magnesium sulfate and 300 g water. The initial water temperature is
10 C. What is the final water temperature after mixing? The density of water is 1.0 g/mL.
Data: Enthalpy of solution(MgSO4)= 91.2 kJ mol-1
Cp(water) = 75.3 J mol-1 K-1
a) Tf = +30 C
b) Tf = +40 C
c) Tf = +50 C
d) Tf = +70 C
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14. Calculate the change in enthalpy for the combustion of 1 mol (304.5 g) of arachidonic acid?
The combustion reaction is:
C20H32O2 + 27 O2(g)  20 CO2(g) + 16 H2O(l)
Data: Enthalpies of Formation:
 C20H32O2
-636 kJ/mol
 CO2
-394 kJ/mol
 H2O(liq)
-286 kJ/mol
a) -11,820 kJ
b) -11,426 kJ
c) -11,534 kJ
d) -12,392 kJ
15. 50 ml of 1.0 M HCl and 50 ml of NaOH are combined in a constant pressure calorimeter. The temperature of
the solution is observed to rise from 21.0 °C to 27.5 °C. Calculate the enthalpy change for the reaction (assume
density is 1.0 gram/ml, and that the specific heat of the solution is that of water).
a) - 2717 J
b) + 2717 J
c) - 5434 J
d) + 5434 J
e) - 54340 J/mol
16. A 1.00-g sample of octane is burned in a calorimeter that contains 1.20 kg of water, and the temperature of the
water and the bomb rises from 25.00 oC to 33.20 oC. If the heat capacity of the bomb, Cbomb, is known to be
837J/oC, then the heat transferred in the combustion of the 1.00-g sample of C8H18 is:
a) - 441.2 ×10 3 J
b) 6.86 ×10 3J
c) - 48.1 ×10 3J
d) - 434.34 ×10 3 J
Useful Formulas
Heat capacity = Specific heat × Mass
Cpo = Specific heat × Molar mass
Q= Heat capacity × ∆T
Q  mcT
 ∆H
=  ∆S
∆Hf o =
∆S o
∆G = ∆H
o
(products)
o
 ∆H
–  ∆S
(products)
– T∆S
–
(reactants)
(reactants)
o
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