Chapter 5 Review
Additional Questions
1) Bricks in a fireplace will absorb heat and release it long after the fire has gone out. A student
conducted an experiment to determine the specific heat capacity of a brick. Based on the
evidence obtained in this experiment, 16 kJ of energy was transferred to a 938-g brick as the
temperature of the brick changed from 19.5°C to 35.0°C. Calculate the specific heat capacity of
the brick.
2) Propane gas is used to heat a tank of water. If the tank contains 200.0 L of water, what mass
of propane will be required to raise its temperature from 20.0°C to 65.0°C? (∆Hcomb for propane =
–2220 kJ/mol)
3) When glucose is allowed to ferment, ethanol and carbon dioxide are produced. Given that the
enthalpies of combustion of glucose and ethanol are -2813 kJ/mol and -1369 kJ/mol respectively, use
Hess’s law to calculate the enthalpy change when 0.500 kg of glucose is allowed to ferment.
4) The molar enthalpy of combustion of natural gas is -802 kJ/mol. Assuming 100% efficiency and
assuming that natural gas consists only of methane, what is the minimum mass of natural gas that
must be burned in a laboratory burner at SATP to heat 3.77 L of water from 16.8°C to 98.6°C?
5) Ammonia forms the basis of a large fertilizer industry. Laboratory research has shown that nitrogen
from the air reacts with liquid water using sunlight and a catalyst to produce ammonia and oxygen.
This research, if technologically feasible on a large scale, may lower the cost of producing ammonia
fertilizer.
(a)
Determine the enthalpy change of the reaction, using a chemical equation balanced
with whole number coefficients.
(b)
Calculate the quantity of solar energy needed to produce 1.00 kg of ammonia.
(c)
If 3.60 MJ of solar energy is available per square metre each day, what area of solar
collectors would provide the energy to produce 1.00 kg of ammonia in one day?
6) Two reactions are given by the following equations:
X(g) + W(g) → Z(g) + Y(g) + 30.0 kJ
Z(g) + Y(g) + 25 kJ → P(g)
Find the ∆Hº value for the reaction P(g) → X(g) + W(g).
7) When CO2(s) sublimes (changes directly from a solid to a gas) at –90ºC, ∆Hsub is 16.20 kJ/mol.
What is the mass of CO2(s) that must have undergone this process of sublimation if 186.0 kJ of heat is
absorbed?
8) Use the data table of standard enthalpies of formation to help determine the enthalpy of reaction for
each of the following reactions.
(a) N2O4(g) + 3CO(g) → N2O(g) + 3CO2(g)
(b) 4FeS2(s) + 11O2(g) → 8SO2(g) + 2Fe2O3(s)
9)
a) Write the balanced equation for the complete combustion of glucose, C6H12O6(s), to form
carbon dioxide gas and water.
b) When a 2.000 g sample of glucose is burned in a calorimeter, the temperature of 200.00 g
of water rises by 37.3ºC. What is the molar enthalpy of combustion of glucose?
10) Using the data table on standard enthalpies of formation, determine the heat absorbed when a
5.00 g sample of Fe2O3(s) undergoes the following reaction.
6Fe2O3(s) → 4Fe3O4(s) + O2(g)
11) Predict whether the entropy will be positive or negative for each of the following changes and
determine.
a. Ag+(aq) + Cl-(aq) → AgCl(s)
b. C2H4(g) + 3O2 → 2CO2(g) + 2H2O(g)
c. I2(s) → I2(g)
d. NaCl(s) → Na+(aq) + Cl-(aq)
12) Replace each question mark with the correct information
a)
b)
c)
d)
e)
f)
Srxn
+
?
0
?
+
Hrxn
0
+
?
0
+
Grxn
?
+
?
Comment
?
Spontaneous
Non spontaneous
Spontaneous
?
TS>H
13)
Answers:
1) 1.10 J/g0C
2) 748 g
3)-208 kJ
4) 25.7 g
5) a) 1531.2 kJ
b) 2.25 x 104 kJ
c) 6.25 m2
6) 5 kJ
7) 506 g
8)a) –778.5 kJ
b) –3310 kJ
9) a) C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(g)
b) Hf = -2.81 x 103 kJ/mol
10) 2.46 kJ
11) a) neg
b) neg
c) pos
d) pos
12) a) spontaneous b) + c) + d) – e) -, not spontaneous
f) 13) a) -91.2 kJ (spont)
b) -1299.6 kJ (spont)
c) -1238.2 kJ (spont)
0