27. Which of the following processes is endothermic?
a. forming snowflakes from liquid
rain
b. making I2 crystals from vapor
c. condensing steam
d. vaporizing CO2 from dry ice
28. A change producing 6.72 J supplies
a. 28.1 cal.
b. 28.1 kcal. c.
1.61 kcal. d. 1.61
cal.
29. Which of the following would result in
a +400 J change in the internal energy of a system?
a. A system absorbs 800
J of heat and does 400 J of work.
b. A system gives off
800 J of heat and does 400 J of work.
c. A system absorbs 800
J of heat and 400 J of work is done on the system.
d. A system gives off
800 J of heat and 400 J of work is done on the system.
30. The thermal energy required to change
the temperature of an object by 1°C is called its
a. heat capacity.
b. specific heat. c.
entropy. d. enthalpy.
31. The thermal energy required to change
the temperature of one gram of a substance by 1°C is called its
a. heat capacity.
b. specific heat.
c. entropy. d.
enthalpy.
32. Samples of several substances cooled
from 65°C to 24°C; the sample that released the most
thermal energy
was the one with
a. the smallest heat capacity.
b. the largest heat capacity.
33. Which of the following statements is
TRUE of DH for the process NaCl(s) --->NaCl(l)
?
[HINT:
Notice the states of NaCl. (s) = Solid & (l) = Liquid]
a. DH is positive
and the process is endothermic.
b. DH is negative and the process is endothermic.
c. DH is positive
and the process is exothermic.
d. DH is negative and the process is exothermic.
34. Which of the following two reactions
would most likely require heat for the reaction to take place?
a. Reactants ---> Products
DH° = +100 kJ
b. Reactants ---> Products
DH° = -100 kJ
35. Which of the following statements is
true for the thermochemical equation shown below?
2 SO3(g) --> 2 SO2(g) + O2(g)
DH = +197.78 kJ
a. The reaction is exothermic.
b. The reaction results
in 198 kJ of evolved heat when 2.00 g of SO3 react.
c. The reaction requires
198 kJ of heat to produce 2.00 mol of SO2.
d. The reaction vessel
would feel warm.
36. The substance for which DHof
is NOT zero is
a. Na(s).
b. Hg(s). c.
Ne(g). d. Br2(l).
37. Based upon the following thermochemical
equation, how much Cl2 must be reacted to produce 502 kJ of
heat?
CH4(g) + 4 Cl2(g) --> CCl4(g) + 4 HCl(g)
DH = -402 kJ.
a. 56.8 g
b. 88.5 g c.
227 g d. 354 g
38. The heats of combustion in kJ/mol are
in brackets following the compounds in the list below.
The substance
that would supply the most thermal energy for each gram burned is
a. CH4 [-890].
b. C2H6 [-1560].
c. CH3OH [-727].
d. C2H5OH [-1367].
39. Calculate the heat of combustion of naphthalene,
C10H8, in kilojoules per gram based upon the following
information.
A 1.435 g sample of naphthalene, C10H8, is burned
in a calorimeter which has a heat
capacity of 10.16
kJ/oC. The temperature of the calorimeter increased from
20.17oC to 25.84oC.
a. -40.14 kJ/g
b. -56.33 kJ/g c.
-73.82 kJ/g d. -95.06
kJ/g
40. Thermal energy gained or lost when a
change takes place under constant pressure is called the
a. temperature change.
b. enthalpy change. c. heat capacity.
d. thermochemical equation.
41. How many kilojoules of heat must be added
to 500.0 g of iron to raise its temperature from 25.0°C to 1535.0°C?
(specific
heat of iron = 0.449 J/g°C)
a. 500.0 kJ
b. 339.0 kJ c.
253.8 kJ d. 736.3
kJ
42. A 150.0 g sample of metal at 80.0oC
is added to 150.0 g of water at 20.0oC. The temperature
of the water rises to
23.3oC.
Assuming no heat loss, what is the specific heat of the metal? (Specific
heat of water is 4.18 J/goC.)
a. 0.96 J/goC
b. 0.48 J/goC
c. 0.72 J/goC
d. 0.24 J/goC
43. Which of the following statements is
FALSE?
a. The reaction vessel
cools when an endothermic reaction occurs.
b. An exothermic reaction
is characterized by a negative enthalpy value.
c. Heat is added to the
system when an endothermic reaction occurs.
d. An endothermic reaction
causes the surroundings to absorb heat.
44. Given the thermochemical equation:
2 SO(g) + O2(g) ---> 2 SO2(g) DH
= -192.8 kJ
what is DH
for the following reaction?
SO2(g)
---> SO(g) + 1/2 O2(g) DH =
?
a. -385.6 kJ
b. -96.4 kJ. c.
+96.4 kJ. d. -192.8
kJ.
45. The heat of combustion of benzene (C6H6)
is -3271 kJ/mol:
C6H6(l)
+ 15/2 O2(g) ----> 6 CO2(g) + 3 H2O(l)
DH = -3271 kJ
How much heat is liberated
when 234.0 g of benzene are burned?
a. -3271 kJ
b. -256 kJ c.
-9798 kJ d. -4370
kJ
46. The standard enthalpy of formation
a. the thermal energy
change when a reaction occurs under constant pressure.
b. the thermal energy
change for a reaction that forms one mole of a substance (in its standard
state)
from the elements of which it is made (in their standard states).
c. the thermal energy
transfer that results from a difference in temperature.
d. the amount of thermal
energy required to heat one mole of a substance 1 °C.
47. The reaction which corresponds to the
standard heat of formation (DHof)
of lead sulfate, PbSO4(s) is:
a. Pb2+(aq)
+ SO42-(aq) ---> PbSO4(s)
b. Pb(g) + S(g) + 2O2(g)
---> PbSO4(g)
c. Pb(s) + S(s) + 2O2(g)
---> PbSO4(s)
d. Pb(l) + S(l) + 2O2(g)
---> PbSO4(s)
48. Given the following data,
C(graphite) + O2(g) ---> CO2(g) DH
= -393 kJ
C(diamond) + O2(g) ---> CO2(g) DH
= -395 kJ
find
the heat required for the conversion of graphite to diamond.
C(graphite)
---> C(diamond) DH = ?
a. -788 kJ/mol
b. +788 kJ/mol c.
-2 kJ/mol d. +2 kJ/mol
49. Calculate DHo
for the combustion of C3H6(g):
2 C3H6(g)
+ 9 O2(g) ---> 6 CO2(g) + 6 H2O(l)
DHo = ?
Standard
heats of formation (DHof)
values are as follows:
C3H6(g)
= +21 kJ/mol
CO2(g) = -394 kJ/mol
H2O(l) = -286 kJ/mol
a. +4122 kJ
b. -4038 kJ c.
+4038 kJ d. -4122
kJ
50. Calculate DH
for the following reaction:
C2H2(g)
+ 2 H2(g) ----> C2H6(g) DH
= ?
Given:
2 C2H2(g) + 5 O2(g) ----> 4 CO2(g)
+ 2 H2O(l) DH
= -622 cal
2 C2H6(g) + 7 O2(g) ----> 4 CO2(g)
+ 6 H2O(l) DH
= -746 cal
H2(g) + 1/2 O2(g) ----> H2O(l)
DH = -68 cal
a. -74 cal
b. -1300 cal c.
+1436 cal d. -972
cal