Chemical Thermodynamics (CHMS4208)

BSc, Chemistry - CHMS

Semester: Resit

Level: 400

Year: 2018

Answers (200 )
REPUBLIC OF CAMEROON THE UNIVERSITY OF BAMENDA
Peace-Work-Fatherland
P. O. BOX 39 Bambili
School/Faculty: _FS__ Department:_CHEMISTRY_Lecturer(s):_NDIKONTAR.___
Course Code: _CHMS4208_______ Course Title: CHEMICAL THERMODYNAMICS
Date: _13/09/2018_______Halls: __ ASANJI________Time: 10:30-12:00 (1.5 H)__
Instructions:Answer all questions
R = 8.314 J K
-1
mol
-1
= 0.08206 L atm K
-1
mol
-1
= 1.987 cal K
-1
mol
-1
1. (20 marks) Consider the following equilibrium: AgCl. 3/2NH
3
(s) ⇌AgCI(s) + 3/2 NH
3
(g). Given the
following thermodynamic data at 298 K:
-
pressure of NH
3
in equilibrium with the two solid phases, P = 0.276 atm
-
∆
= 55 cal K
-1
mol
-1
-
specific heat capacities at constant pressure in cal K
-1
mol
-1
: NH
3
(g): 8.5; AgCl. 3/2NH
3
(s): 19.6;
AgCI(s): 12.1 (neglect their variations with temperature)
i. Calculate the equilibrium constant K
p
and the enthalpy change of the reaction at 298 K.
ii. 0.02 mol of AgCI(s) are introduced into a vessel of 5 L maintained at 298 K. What is the minimum
amount of NH
3
that must be added into the vessel for the complete conversion of AgCI(s) into AgCl.
3/2NH
3
(s)?
2. (15 marks) In the liquid phase, allocimen (A) gives the dimer (D) by the reversible reaction: A⇌
D. The normal enthalpy of vaporization of A is 9656 cal/mol; its normal boiling is 177.0’C and that of D is
189.5 °C. The mixture A + D constitutes an ideal solution. The density is constant and equal to 0.694
g/cm
3
. Molar mass of A is 136 g/mol. Liquid allocimen is put in a flask and after removing all air, the flask
is sealed and heated to 189.5’C. When equilibrium is attained, 89% of A has dimerised. Calculate:
i. the mole fraction x
A
of the monomer in equilibrium at 189.5’C.
ii. the normal enthalpy of vaporisation of the dimer D, supposing that Trouton's rule is valid.
iii. the vapour pressure of pure A at 189.5’C, using the Clausius-Clapeyron equation.
iv. the pressure inside the sealed flask at equilibrium at 189.5’C
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