H midyear review ch 6
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Timothy Koby
ChemistryH, section Period 11, 20042005
Instructor: Victoria Hubinger
Watchung Hills Regional High School
About this Assignment
Due: Monday, January 24, 2005 07:25 AM
EST
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1. [Chang7 6.P.017.] A piece of metal of mass 373 g has a heat capacity of 71.8 J/°
C. What is the specific heat of this metal?
.192
J/g · °C
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2. [Chang7 6.P.021.] A 0.1469 g sample of solid magnesium is burned in a constantvolume bomb calorimeter that has a heat capacity of 1769 J/°C. The calorimeter
contains exactly 341 g of water, and the temperature increases by 1.126°C.
Calculate the heat given off by the burning Mg, in kJ/g and in kJ/mol.
24.5
kJ/g
595
kJ/mol
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3. [Chang7 6.P.019.] Calculate the amount of heat liberated (in kJ) from 391 g of
mercury when it cools from 64.0°C to 13.0°C.
-2.77
kJ
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4. [Chang7 6.P.035.] Calculate the heat of decomposition for this process at
constant pressure and 25°C. (Look up the standard enthalpy of formation of the
reactant and products in Table 6.3 and Appendix 3.)
267.1
kJ
BaCO3(s)
BaO(s) + CO2(g)
Notes
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H midyear review ch 6
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5. [Chang7 6.P.037.] Calculate the heats of combustion for the following reactions
from the standard enthalpies of formation listed in Appendix 3.
(a) 2 H2(g) + O2(g)
2 H2O(l)
-571.6
kJ
(b) 2 C6H6(l) + 15 O2(g)
-6534.88
12 CO2(g) + 6 H2O(l)
kJ
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6. [Chang7 6.P.045.] From the data shown below, calculate the enthalpy change for
the following transformation.
S(rhombic)
S(monoclinic)
(Monoclinic and rhombic are different allotropic forms of elemental sulfur.)
S(rhombic) + O2(g)
S(monoclinic) + O2(g)
SO2(g)
SO2(g)
H°rxn = -296.06 kJ
H°rxn = -296.36 kJ
Notes
.30
kJ
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7. [Chang7 6.P.047.] Given the following heats of combustion.
CH3OH(l) + 3/2 O2(g)
CO2(g) + 2 H2O(l)
H°rxn = -726.4 kJ
CO2(g)
H°rxn = -393.5 kJ
C(graphite) + O2(g)
H2O(l)
H°rxn = -285.8 kJ
H2(g) + 1/2 O2(g)
Calculate the enthalpy of formation of methanol (CH3OH) from its elements.
C(graphite) + 2 H2(g) + 1/2 O2(g)
CH3OH(l)
Notes
-238.7
kJ
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8. [Chang7 6.P.073.] Methanol (CH3OH) is an organic solvent and is also used as a
fuel in some automobile engines. From the following data, calculate the standard
enthalpy of formation of methanol.
2 CH3OH(l) + 3 O2(g)
-238.7
2 CO2(g) + 4 H2O(l)
H°rxn = -1452.8 kJ
kJ/mol
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9. [Chang7 6.TB.012a.] Consider the following reaction.
2 CH3OH(l) + 3 O2(g)
4 H2O(l) + 2 CO2(g)
H = -1452.8 kJ
What is the value of H if the equation is multiplied throughout by 2?
-1452.8 kJ
-2905.6 kJ
Notes
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10. [Chang7 6.TB.014.] Consider two metals A and B, each having a mass of 100 g
and an initial temperature of 20°C. The specific heat of A is larger than that of B.
Under the same heating conditions, which metal would take longer to reach a
temperature of 21°C?
Metal B
Metal A
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11. [Chang7 6.TB.020.] A sheet of gold weighing 10.0 g and at a temperature of 18.0°
C is placed flat on a sheet of iron weighing 20.0 g and at a temperature of 55.6°C.
What is the final temperature of the combined metals? Assume that no heat is lost
to the surroundings. (Hint: The heat gained by the gold must be equal to the heat
lost by the iron.)
36.8°C.
50.7°C.
46.3°C.
62.0°C.
Notes
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12. [Chang7 6.TB.021b.] A 0.1375 g sample of solid magnesium is burned in a
constant-volume bomb calorimeter that has a heat capacity of 1769 J/°C. The
calorimeter contains exactly 300 g of water, and the temperature increases by
1.126°C. Calculate the heat given off by the burning Mg in kJ/mol.
1.02 103 kJ/mol
603 kJ/mol
1.14 103 kJ/mol
11.4 kJ/mol
Notes
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13. [Chang7 6.TB.022.] A quantity of 2.00 102 mL of 0.862 M HCl is mixed with
2.003102 mL of 0.431 M Ba(OH)2 in a constant-pressure calorimeter that has a
heat capacity of 453 J/°C. The initial temperature of the HCl and Ba(OH)2 solutions
is the same at 20.48°C. For the following process the heat of neutralization is -56.2
kJ.
H+(aq) + OH-(aq)
H2O(l)
What is the final temperature of the mixed solution?
29.6°C
43.2°C
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H midyear review ch 6
25.0°C
15.9°C
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14. [Chang7 6.TB.029.] Which of the following standard enthalpy of formation values
is not zero at 25°C? (Select all that apply.)
Ne(g)
S8(s)
✔
Hg(l)
H(g)
Na(s)
CH4(g)
Notes
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15. [Chang7 6.TB.030.] The
values of the two allotropes of oxygen, O2 and
O3, are 0 and 142.2 kJ/mol, respectively, at 25°C. Which is the more stable form at
this temperature?
O2
Neither are stable.
O3
Both O2 and O3 are equally stable.
Notes
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16. [Chang7 6.TB.032b.] Predict the value of
to zero) for Br2(l) at 25°C.
(greater than, less than, or equal
less than zero
greater than zero
equal to zero
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17. [Chang7 6.TB.033.] In general, compounds with negative
values are more
values. H2O2(l) has a negative
(see
stable than those with positive
Table 6.3). Why, then, does H2O2(l) have a tendency to decompose to H2O(l) and
O2(g)?
H2O2(l) has a more negative standard enthalpy of formation than does
H2O(l).
Forming two products drives the reaction.
Forming O2(g) drives the reaction.
H2O(l) has a more negative standard enthalpy of formation than does
Notes
H2O2(l).
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H midyear review ch 6
Table 6.3
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18. [Chang7 6.TB.039c.] Methanol, ethanol, and n-propanol are three common
alcohols. When 1.00 g of n-propanol (C3H7OH)is burned in air, -33.4 kJ of heat is
liberated. Calculate the heat of combustion of n-propanol in kJ/mol.
1.97 103 kJ/mol
-2.01 103 kJ/mol
2.01 103 kJ/mol
-1.97 103 kJ/mol
Notes
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