,DOWNLOAD THE Test Bank for Elements of Physical Chemistry 7th Edition
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
Test bank: Focus 02
Type: multiple choice question
Title: Focus 02 - Question 01
01) Calculate the expansion work done on the system when exactly 1 mol of solid ammonium
chloride, NH4Cl, decomposes completely to yield gaseous ammonia, NH3 and hydrogen
chloride, HCl at a temperature of 1250 K. Treat the expansion as irreversible and the gases
formed as perfect.
Feedback: The work done on a system when it expands against a constant pressure is given
by eqn 2A.1a
𝑤 = −𝑝ex Δ𝑉
The decomposition of exactly 1 mol of solid ammonium chloride
NH4Cl(s) → NH3(g) + HCl(g) yields 2 mol of gas. We may assume that the volume of the
solid ammonium chloride is negligible in comparison with the volume of the gas produced.
The change in volume on decomposition is therefore
Δ𝑉 = 𝑉f − 𝑉i ≈ 𝑉f
Treating the gas as perfect, so that
𝑛𝑅𝑇
𝑉f =
𝑝ex
then
𝑛𝑅𝑇
𝑤 = −𝑝ex ×
𝑝ex
= −𝑛𝑅𝑇
= −(2.00 mol) × (8.3145 J K −1 mol−1 ) × (1250 K)
= −20.8 × 103 J
= −𝟐𝟎. 𝟖 𝐤𝐉
Page reference: 41
a. –15.4 kJ
b. –4.96 kJ
c. –16.6 kJ
*d. –20.8 kJ
Type: multiple choice question
Title: Focus 02 - Question 02
02) Calculate the heat transferred to the system when 1.00 mol of a perfect gas expands
reversibly at a constant temperature of 25°C so that its volume doubles.
Feedback: For the isothermal expansion of a perfect gas, eqn 2B.4 shows that the heat
transferred and work done are related by
𝑞 = −𝑤
and so, using eqn 2A.2 for a reversible expansion, we obtain eqn 2B.5,
𝑞 = −𝑛𝑅𝑇𝑙𝑛𝑉f /𝑉i
For this expansion,
𝑉f /𝑉i = 2
so that
𝑞 = −(1.00 mol) × (8.3145 J K −1 mol−1 ) × (273 + 25)K × ln 2
= −1.72 × 103 J
= −𝟏. 𝟕𝟐 𝐤𝐉 𝐦𝐨𝐥−𝟏
Page reference: 43, 51
a. –144 J
b. –746 J
*c. –1.72 kJ mol–1
d. 2.48 kJ
Type: multiple choice question
Title: Focus 02 - Question 03
08) The constant pressure molar heat capacity of zinc is 25.40 J K–1 mol–1 at 298 K.
Calculate the constant pressure specific heat capacity of zinc at this temperature.
© Oxford University Press, 2017.
mynursytest.store
,DOWNLOAD THE Test Bank for Elements of Physical Chemistry 7th Edition
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
Feedback: Specific heat capacity is defined as the heat capacity per unit mass of sample
𝐶s = 𝐶/𝑚
and so,
𝐶s = 𝐶𝑝,m /𝑀
For zinc, the molar mass is
𝑀 = 65.37 g mol−1
so that
𝐶s = 𝐶𝑝,m /𝑀
= (25.40 J K −1 mol−1 ) / (65.37 × 10−3 kg mol−1 )
= 𝟑𝟖𝟖. 𝟔 𝐉 𝐊 −𝟏 𝐤𝐠 −𝟏
Page reference: 48
a. 1.660 kJ K–1 kg–1
*b. 388.6 J K–1 kg–1
c. 17.09 J K–1 kg–1
d. 33.71 J K–1 kg–1
Type: multiple choice question
Title: Focus 02 - Question 04
03) The molar heat capacity of solid aluminium is 24.4 J K–1 mol–1 at 25°C. Calculate the
change in internal energy when 1.00 mol of solid aluminium is heated from a temperature of
20°C to 30°C.
Feedback: Heat capacity is defined by eqn 2C.4a and so we can write
∆𝑈 = 𝐶𝑉 Δ𝑇
For a solid,
𝐶𝑝 ≈ 𝐶𝑉
and so we do not need to worry about the distinction between the heat capacity at constant
volume and pressure. We may also reasonably assume that the heat capacity does not vary
over the range of temperature. A change in temperature from 20 °C to 30 °C means
Δ𝑇 = +10 K
Thus
Δ𝑈 = 𝑛𝐶m Δ𝑇
= (1.00 mol) × (24.4 J K –1 mol−1 ) × (10 K)
= 𝟐𝟒𝟒 𝐉
Page reference: 54
*a. 244 J
b. 24.4 J
c. 171 J
d. 327 J
Type: multiple choice question
Title: Focus 02 - Question 05
04) The constant pressure molar heat capacity of ammonia, NH3, has been found to vary with
temperature according to the relation
𝐶𝑝,m / J K −1 mol−1 = 𝑎 + 𝑏𝑇 + 𝑐/𝑇 2
with a = 29.73, b = 25.1 10 K–1 and c = –1.55 105 K2. Calculate the value of the constant
–3
pressure molar heat capacity at 25.0 °C.
Feedback: The constant pressure molar heat capacity may be calculated by direct
substitution. We must, however, remember to convert the temperature to units of kelvin.
Thus
𝑇 = (273.15 + 25.0)K = 298.15 K
so that
𝑐
𝐶𝑝,m /( J K −1 mol−1 ) = 𝑎 + 𝑏𝑇 + 2
𝑇
= 29.73 + {(25.1 × 10−3 K −1 ) × (298.15 K)} − {1.55 × 105 K 2 /(298.15 K)2 }
= 35.47
Thus
© Oxford University Press, 2017.
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, DOWNLOAD THE Test Bank for Elements of Physical Chemistry 7th Edition
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
𝐶𝑝,m = 𝟑𝟓. 𝟒𝟕 𝐉 𝐊 −𝟏 𝐦𝐨𝐥−𝟏
Page reference: 59
a. 217.6 J K–1 mol–1
b. 29.73 J K–1 mol–1
*c. 35.47 J K–1 mol–1
d. 657.2 J K–1 mol–1
Type: multiple choice question
Title: Focus 02 - Question 06
05) In the calibration step of a thermochemistry experiment, a current of 117 mA, from a
24.0 V source was allowed to flow through the electrical heater for 247 s and was found to
result in an increase in the temperature of the calorimeter and its contents of +1.25 K.
Calculate the heat capacity of the calorimeter and its contents.
Feedback: Heat capacity is defined by eqn 2B.1
𝐶 = 𝑞/Δ𝑇
For an electrical heater, the amount of heat transferred is given by eqn 2B.3
𝑞cal = 𝐼𝒱𝑡
so that, if we combine these two expressions
𝐶 = 𝐼𝒱𝑡/ Δ𝑇
= (117 × 10−3 A) × (24.0 V) × (247 s) / (1.25 K)
= 𝟓𝟓𝟓 𝐉 𝐊 −𝟏
Page reference: 50
a. 694 J K–1
b. 277 J K–1
*c. 555 J K–1
d. 867 J K–1
Type: multiple choice question
Title: Focus 02 - Question 07
06) The constant pressure molar heat capacity of methane, CH4, is 35.31 J K–1 mol–1 at
temperatures close to 298 K. Calculate the enthalpy change when 2.00 mol of methane is
heated from a temperature of 278 K to 318 K.
Feedback: We may calculate the change in enthalpy on heating by rearranging eqn 2B.5
Δ𝐻 = 𝐶Δ𝑇
if we know that the heat capacity is constant and does not vary with temperature. We know
the constant pressure molar heat capacity, so that
𝐶 = 𝑛 𝐶𝑝,m
Δ𝐻 = 𝑛 𝐶𝑝,m Δ𝑇
= (2.00 mol) × (35.31 J K −1 mol−1 ) × (318 − 278) K
= 2830 J = 𝟐. 𝟖𝟑 𝐤𝐉
Page reference: 59
a. 21.2 kJ
b. 353 J
c. 1.41 kJ
*d. 2.83 kJ
Type: multiple choice question
Title: Focus 02 - Question 08
07) The constant pressure molar heat capacity of argon is 20.79 J K–1 mol–1 at 298 K. Predict
the value of the constant volume molar heat capacity of argon at this temperature.
Feedback: For a perfect gas, eqn 2D.7, shows that
𝐶𝑝,m − 𝐶𝑉,m = 𝑅
and hence
𝐶𝑉,m = 𝐶𝑝,m − 𝑅
= (20.79 J K −1 mol−1 ) − (8.3145 J K −1 mol−1 )
= 𝟏𝟐. 𝟒𝟖 𝐉 𝐊 −𝟏 𝐦𝐨𝐥−𝟏
© Oxford University Press, 2017.
mynursytest.store
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
Test bank: Focus 02
Type: multiple choice question
Title: Focus 02 - Question 01
01) Calculate the expansion work done on the system when exactly 1 mol of solid ammonium
chloride, NH4Cl, decomposes completely to yield gaseous ammonia, NH3 and hydrogen
chloride, HCl at a temperature of 1250 K. Treat the expansion as irreversible and the gases
formed as perfect.
Feedback: The work done on a system when it expands against a constant pressure is given
by eqn 2A.1a
𝑤 = −𝑝ex Δ𝑉
The decomposition of exactly 1 mol of solid ammonium chloride
NH4Cl(s) → NH3(g) + HCl(g) yields 2 mol of gas. We may assume that the volume of the
solid ammonium chloride is negligible in comparison with the volume of the gas produced.
The change in volume on decomposition is therefore
Δ𝑉 = 𝑉f − 𝑉i ≈ 𝑉f
Treating the gas as perfect, so that
𝑛𝑅𝑇
𝑉f =
𝑝ex
then
𝑛𝑅𝑇
𝑤 = −𝑝ex ×
𝑝ex
= −𝑛𝑅𝑇
= −(2.00 mol) × (8.3145 J K −1 mol−1 ) × (1250 K)
= −20.8 × 103 J
= −𝟐𝟎. 𝟖 𝐤𝐉
Page reference: 41
a. –15.4 kJ
b. –4.96 kJ
c. –16.6 kJ
*d. –20.8 kJ
Type: multiple choice question
Title: Focus 02 - Question 02
02) Calculate the heat transferred to the system when 1.00 mol of a perfect gas expands
reversibly at a constant temperature of 25°C so that its volume doubles.
Feedback: For the isothermal expansion of a perfect gas, eqn 2B.4 shows that the heat
transferred and work done are related by
𝑞 = −𝑤
and so, using eqn 2A.2 for a reversible expansion, we obtain eqn 2B.5,
𝑞 = −𝑛𝑅𝑇𝑙𝑛𝑉f /𝑉i
For this expansion,
𝑉f /𝑉i = 2
so that
𝑞 = −(1.00 mol) × (8.3145 J K −1 mol−1 ) × (273 + 25)K × ln 2
= −1.72 × 103 J
= −𝟏. 𝟕𝟐 𝐤𝐉 𝐦𝐨𝐥−𝟏
Page reference: 43, 51
a. –144 J
b. –746 J
*c. –1.72 kJ mol–1
d. 2.48 kJ
Type: multiple choice question
Title: Focus 02 - Question 03
08) The constant pressure molar heat capacity of zinc is 25.40 J K–1 mol–1 at 298 K.
Calculate the constant pressure specific heat capacity of zinc at this temperature.
© Oxford University Press, 2017.
mynursytest.store
,DOWNLOAD THE Test Bank for Elements of Physical Chemistry 7th Edition
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
Feedback: Specific heat capacity is defined as the heat capacity per unit mass of sample
𝐶s = 𝐶/𝑚
and so,
𝐶s = 𝐶𝑝,m /𝑀
For zinc, the molar mass is
𝑀 = 65.37 g mol−1
so that
𝐶s = 𝐶𝑝,m /𝑀
= (25.40 J K −1 mol−1 ) / (65.37 × 10−3 kg mol−1 )
= 𝟑𝟖𝟖. 𝟔 𝐉 𝐊 −𝟏 𝐤𝐠 −𝟏
Page reference: 48
a. 1.660 kJ K–1 kg–1
*b. 388.6 J K–1 kg–1
c. 17.09 J K–1 kg–1
d. 33.71 J K–1 kg–1
Type: multiple choice question
Title: Focus 02 - Question 04
03) The molar heat capacity of solid aluminium is 24.4 J K–1 mol–1 at 25°C. Calculate the
change in internal energy when 1.00 mol of solid aluminium is heated from a temperature of
20°C to 30°C.
Feedback: Heat capacity is defined by eqn 2C.4a and so we can write
∆𝑈 = 𝐶𝑉 Δ𝑇
For a solid,
𝐶𝑝 ≈ 𝐶𝑉
and so we do not need to worry about the distinction between the heat capacity at constant
volume and pressure. We may also reasonably assume that the heat capacity does not vary
over the range of temperature. A change in temperature from 20 °C to 30 °C means
Δ𝑇 = +10 K
Thus
Δ𝑈 = 𝑛𝐶m Δ𝑇
= (1.00 mol) × (24.4 J K –1 mol−1 ) × (10 K)
= 𝟐𝟒𝟒 𝐉
Page reference: 54
*a. 244 J
b. 24.4 J
c. 171 J
d. 327 J
Type: multiple choice question
Title: Focus 02 - Question 05
04) The constant pressure molar heat capacity of ammonia, NH3, has been found to vary with
temperature according to the relation
𝐶𝑝,m / J K −1 mol−1 = 𝑎 + 𝑏𝑇 + 𝑐/𝑇 2
with a = 29.73, b = 25.1 10 K–1 and c = –1.55 105 K2. Calculate the value of the constant
–3
pressure molar heat capacity at 25.0 °C.
Feedback: The constant pressure molar heat capacity may be calculated by direct
substitution. We must, however, remember to convert the temperature to units of kelvin.
Thus
𝑇 = (273.15 + 25.0)K = 298.15 K
so that
𝑐
𝐶𝑝,m /( J K −1 mol−1 ) = 𝑎 + 𝑏𝑇 + 2
𝑇
= 29.73 + {(25.1 × 10−3 K −1 ) × (298.15 K)} − {1.55 × 105 K 2 /(298.15 K)2 }
= 35.47
Thus
© Oxford University Press, 2017.
mynursytest.store
, DOWNLOAD THE Test Bank for Elements of Physical Chemistry 7th Edition
Atkins
Atkins & de Paula: Elements of Physical Chemistry 7e
𝐶𝑝,m = 𝟑𝟓. 𝟒𝟕 𝐉 𝐊 −𝟏 𝐦𝐨𝐥−𝟏
Page reference: 59
a. 217.6 J K–1 mol–1
b. 29.73 J K–1 mol–1
*c. 35.47 J K–1 mol–1
d. 657.2 J K–1 mol–1
Type: multiple choice question
Title: Focus 02 - Question 06
05) In the calibration step of a thermochemistry experiment, a current of 117 mA, from a
24.0 V source was allowed to flow through the electrical heater for 247 s and was found to
result in an increase in the temperature of the calorimeter and its contents of +1.25 K.
Calculate the heat capacity of the calorimeter and its contents.
Feedback: Heat capacity is defined by eqn 2B.1
𝐶 = 𝑞/Δ𝑇
For an electrical heater, the amount of heat transferred is given by eqn 2B.3
𝑞cal = 𝐼𝒱𝑡
so that, if we combine these two expressions
𝐶 = 𝐼𝒱𝑡/ Δ𝑇
= (117 × 10−3 A) × (24.0 V) × (247 s) / (1.25 K)
= 𝟓𝟓𝟓 𝐉 𝐊 −𝟏
Page reference: 50
a. 694 J K–1
b. 277 J K–1
*c. 555 J K–1
d. 867 J K–1
Type: multiple choice question
Title: Focus 02 - Question 07
06) The constant pressure molar heat capacity of methane, CH4, is 35.31 J K–1 mol–1 at
temperatures close to 298 K. Calculate the enthalpy change when 2.00 mol of methane is
heated from a temperature of 278 K to 318 K.
Feedback: We may calculate the change in enthalpy on heating by rearranging eqn 2B.5
Δ𝐻 = 𝐶Δ𝑇
if we know that the heat capacity is constant and does not vary with temperature. We know
the constant pressure molar heat capacity, so that
𝐶 = 𝑛 𝐶𝑝,m
Δ𝐻 = 𝑛 𝐶𝑝,m Δ𝑇
= (2.00 mol) × (35.31 J K −1 mol−1 ) × (318 − 278) K
= 2830 J = 𝟐. 𝟖𝟑 𝐤𝐉
Page reference: 59
a. 21.2 kJ
b. 353 J
c. 1.41 kJ
*d. 2.83 kJ
Type: multiple choice question
Title: Focus 02 - Question 08
07) The constant pressure molar heat capacity of argon is 20.79 J K–1 mol–1 at 298 K. Predict
the value of the constant volume molar heat capacity of argon at this temperature.
Feedback: For a perfect gas, eqn 2D.7, shows that
𝐶𝑝,m − 𝐶𝑉,m = 𝑅
and hence
𝐶𝑉,m = 𝐶𝑝,m − 𝑅
= (20.79 J K −1 mol−1 ) − (8.3145 J K −1 mol−1 )
= 𝟏𝟐. 𝟒𝟖 𝐉 𝐊 −𝟏 𝐦𝐨𝐥−𝟏
© Oxford University Press, 2017.
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