School of Chemistry & Physics, University of KwaZulu-Natal
CHEM230: Physical Chemistry
Chemical Thermodynamics: Tutorial #1
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6.
Calculate the work done when 50 g of iron reacts with hydrochloric acid to produce
hydrogen gas in
(a) a closed vessel of fixed volume, and
(b) an open beaker at 25 °C.
[(b) −2.219 kJ]
A chemical reaction takes place in a container of cross-sectional area 100 cm2 with a
loosely fitted piston at one end. As a result of the reaction the piston is pushed out
through 10 cm against an external pressure of 1.0 atm. Calculate the work done by the
system.
[−1.013 × 102 J]
A strip of magnesium of mass 15 g is dropped into a beaker of dilute hydrochloric acid.
Calculate the work done by the system as a result of the reaction given that the
atmospheric pressure is 1.0 atm and the temperature 25 °C.
[−1.528 kJ]
A sample of 1.00 mol H2O (g) is condensed isothermally and reversibly to liquid water
at 100 °C. The standard enthalpy of vaporization of water at 100 °C is
+40.656 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1. Find 𝑤𝑤, 𝑞𝑞, ∆𝑈𝑈 and ∆𝐻𝐻 for this process.
[∆𝐻𝐻 = −40.656 𝑘𝑘𝑘𝑘; 𝑞𝑞 = −40.656 𝑘𝑘𝑘𝑘; 𝑤𝑤 = 3.101 𝑘𝑘𝑘𝑘; ∆𝑈𝑈 = −37.555 𝑘𝑘𝑘𝑘]
The value of 𝐶𝐶𝑃𝑃.𝑚𝑚 for a sample of a perfect gas was found to vary with temperature
according to the expression:
𝐶𝐶𝑃𝑃,𝑚𝑚 (𝐽𝐽 𝐾𝐾 −1 𝑚𝑚𝑚𝑚𝑚𝑚 −1 ) = 20.17 + 0.3665𝑇𝑇/𝐾𝐾
Calculate 𝑤𝑤, 𝑞𝑞, ∆𝑈𝑈 and ∆𝐻𝐻 for one mole of the gas when the temperature is raised from
25 °C to 200 °C at:
(a) Constant pressure, and
(b) Constant volume.
[(a) ∆𝐻𝐻 = 28.25 𝑘𝑘𝑘𝑘; 𝑞𝑞 = 28.25 𝑘𝑘𝑘𝑘; 𝑤𝑤 = −1.455 𝑘𝑘𝑘𝑘; ∆𝑈𝑈 + 26.8 𝑘𝑘𝑘𝑘;
(b) ∆𝑈𝑈 = 26.8 𝑘𝑘𝑘𝑘; ∆𝐻𝐻 = 26.8 𝑘𝑘𝑘𝑘; 𝑤𝑤 = 0]
A 0.020 mol sample of Ar, initially at 25 °C, is adiabatically and reversibly expanded
from 0.50 L to 1.00 L. Calculate the final temperature of the gas. The molar heat capacity
at constant volume is 12.48 𝐽𝐽 𝐾𝐾 −1 𝑚𝑚𝑚𝑚𝑚𝑚 −1.
[𝑇𝑇𝑓𝑓 = 187.9 𝐾𝐾]
CHEM230: Chemical Thermodynamics Tutorial #1
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School of Chemistry & Physics, University of KwaZulu-Natal
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(a)
(b)
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CHEM230: Physical Chemistry
Calculate the final pressure when a sample of argon, initially at a pressure of
100 kPa, expands reversibly and adiabatically to twice its initial volume.
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(𝛾𝛾 = 3 for argon)
For the same sample and starting conditions, what would the final pressure be if
the volume were isothermally doubled?
[(𝑎𝑎) 𝑃𝑃𝑓𝑓 = 31.5 𝑘𝑘𝑘𝑘𝑘𝑘; (𝑏𝑏) 𝑃𝑃𝑓𝑓 = 50 𝑘𝑘𝑘𝑘𝑘𝑘]
Estimate the standard enthalpy of formation of cyclohexane (C6H12) at 400 K given the
following data:
∆𝑓𝑓 𝐻𝐻 ∅ (𝐶𝐶6 𝐻𝐻12 ) = −156 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1 (298 𝐾𝐾)
∆𝑓𝑓 𝐻𝐻 𝜃𝜃 (𝐶𝐶) = 0
∆𝑓𝑓 𝐻𝐻 𝜃𝜃 (𝐻𝐻2 ) = 0
9.
𝜃𝜃 (𝐶𝐶
−1
−1
𝐶𝐶𝑃𝑃.𝑚𝑚
6 𝐻𝐻12 ) = 156.5 𝐽𝐽 𝐾𝐾 𝑚𝑚𝑚𝑚𝑚𝑚
𝜃𝜃 (𝐶𝐶(𝑠𝑠))
𝐶𝐶𝑃𝑃.𝑚𝑚
= 8.527 𝐽𝐽 𝐾𝐾 −1 𝑚𝑚𝑚𝑚𝑚𝑚 −1
𝜃𝜃 (𝐻𝐻
−1
−1
𝐶𝐶𝑃𝑃.𝑚𝑚
2 (𝑔𝑔)) = 28.824 𝐽𝐽 𝐾𝐾 𝑚𝑚𝑚𝑚𝑚𝑚
[∆𝑓𝑓 𝐻𝐻 𝜃𝜃 (𝐶𝐶6 𝐻𝐻12 ) = −162.9 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1 (400 𝐾𝐾)]
When naphthalene is burned in oxygen the reaction is:
𝐶𝐶10 𝐻𝐻8 (𝑠𝑠) + 12𝑂𝑂2 (𝑔𝑔) → 10𝐶𝐶𝑂𝑂2 (𝑔𝑔) + 4𝐻𝐻2 𝑂𝑂(𝑙𝑙)
the standard enthalpy for this reaction is ∆𝑐𝑐 𝐻𝐻 𝜃𝜃 = −5157 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1 .
10.
When 120 mg of naphthalene, C10H8(s), was burned in a bomb calorimeter, the
temperature rose by 3.05 K. Calculate the heat capacity of the calorimeter, given the
molar mass of naphthalene is 128.18 g.
[1.58 𝑘𝑘𝑘𝑘 𝐾𝐾 −1 ]
Methane, considered as an ideal gas, initially at 25 °C and at 1 bar pressure is heated at
constant pressure until its volume has doubled. The molar heat capacity at constant
pressure varies with temperature and is given by:
𝐶𝐶𝑃𝑃.𝑚𝑚 (𝐽𝐽 𝐾𝐾 −1 𝑚𝑚𝑚𝑚𝑚𝑚 −1 ) = 22.34 + 48.1 × 10−3 𝑇𝑇/𝐾𝐾
Calculate ∆𝐻𝐻 for the expansion process.
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[13.064 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1]
A kettle containing 0.500 kg of boiling water is heated until evaporation is complete.
Calculate the work, w, the heat, q, and the change in internal energy, ∆𝑈𝑈, for the process.
The density of water at 100 °C is 958.39 𝑘𝑘𝑘𝑘 𝑚𝑚3 and its molar enthalpy of vaporization
is 40.6 𝑘𝑘𝑘𝑘 𝑚𝑚𝑚𝑚𝑚𝑚 −1 . The molar mass of water is 18.016 𝑔𝑔 𝑚𝑚𝑚𝑚𝑚𝑚 −1and steam may be treated
as a perfect gas.
[𝑤𝑤 = −86.047 𝑘𝑘𝑘𝑘; ∆𝑈𝑈 = 1041 𝑘𝑘𝑘𝑘]
CHEM230: Chemical Thermodynamics Tutorial #1
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