Get premium membership and access revision papers, questions with answers as well as video lessons.
Chem 322: Physical Chemistry Iii Question Paper
Chem 322: Physical Chemistry Iii
Course:Bachelor Of Education Science
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
THIRD YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF EDUCATION (SCIENCE)
CHEM 322: PHYSICAL CHEMISTRY III
STREAMS: B.ED (SCIENCE) TIME: 2 HOURS
DAY/DATE: WEDNESDAY 7/8/2013 2.30 P.M. – 4.30 P.M.
INSTRUCTIONS:
Answer Question ONE and any other TWO Questions.
USEFUL DATA:
In (1±x)=±x-x^2/2±x^3/3-x^4/4±---.
R = 0.0821 dm3atm k-1mol-1 = 8.314Jk-1mol-1 = 1.987 Cal k-1mol-1
1 atm = 1.01325 x 105 N m-2 = 101325 Jm-3
1Nm = 1J, 1dm3 = 10-3 m3
Cp = R mol-1 deg-1
Fe = 55.88g mol-1
0oC = 273 k = 31.7oF
Enthalpy of fusion of ice = 333 J g-1
Specific heat capacity of water = 4.19J g-1k-1
For ideal gasdU = (dU/dT)_v dT=nCv dT
QUESTION ONE (30 MARKS)
(a) (i) Differentiate between open, closed and isolated systems with help of well
labelled diagrams. [1 ½ marks]
(ii) Write short notes on a state of a system. [3 marks]
(iii) State and explain the properties of state function. [3 marks]
(b) (i) Show that, work in a reversible process is more than in an irreversible
process. [3 marks]
(ii) One mole of oxygen at 300k expands isothermally from 3 atmospheres to 1 atmosphere. Assuming that oxygen behaves ideally, calculate W in Joules if the expansion is (a) reversible. [1 ½ marks]
(b) Single step against a constant pressure of 1 atmosphere. [½ mark]
(c) (i) Explain why in an isothermal process the temperature of a system remains
constant while in an adiabatic process, temperature must change.
[2 marks]
(ii) 10.0g of ice at 273 k is added to coffee cup calorimeter containing 100.0g of water at 303k. The heat capacity of the calorimeter is 10.0J k-1. What is the final temperature of the water in the cup? [3 marks]
(d) (i) Use the data below to show whether the reaction 2SO2(g) +
O2(g)?2SO3(g) should “occur spontaneously”.
Substance 02(g) SO2(g) SO3(g)
DGoF(KJmol-1) 0.0 -300.4 -370.4
[2 marks]
(ii) When potassium iodide dissolves in water the mixture becomes cool. For this change, which is of a larger magnitude T S or H? [2 marks]
(iii) Cars, trucks, and other machines that use gas or diesel engines for power have cooling systems. In terms of thermodynamics what makes these cooling systems necessary? [1 mark]
(e) (i) A solid body initially at a higher temperature is left in air. It is
spontaneously cool down to room temperature. Does the free energy increase, decrease or remain constant? Does your calculation contradict the second law of thermodynamics? Give reasons for your answer.
[2 ½ marks]
(ii) Show that T2= T1
foradiabatic irreversible changes. [2 marks]
(iii) A certain diatomic gas Cp = 29.3J k-1 mol-1 expands adiabatically from an initial state, V1 = 10-2m3, P1 = 100 atm and T1 = 400k to the final state until the pressure is 1 atm. Calculate the entropy change for the gas if the expansion is
Reversible [ ½ mark]
Irreversible against a constant external pressure of 1 atm. Assume ideal behaviour for the gas and temperature independence for the heat capacity in this temperature range. {Cv = 20.986 J k-1 mol-1}
[2 ½ marks]
QUESTION TWO (20 MARKS)
(a) With reasons explain whether the following statements are correct or incorrect.
H is a state function. [1 mark]
U remains constant in every isothermal process in a closed system.
[2 marks]
If a closed system at rest in the absence of external fields undergoes an adiabatic process that has W = 0, then the temperature of the system must remain constant. [2 marks]
For a closed system doing mechanical work only, a constant pressure that has Q>0 must have T>0.
(b) Derive the following relations for an ideal gas undergoing adiabatic reversible changes
TVY-1 = Qp constant [3 marks]
PVY = a constant [1 mark]
[1 mark]
(i) Calculate W for the adiabatic reversible expansion of 2 moles of an ideal
gas at 273.2k and 20 atm to a final pressure of 2 atm. [3 marks]
(ii) An engine operating between 150oC takes 500J heat from a high temperature reservoir. Assuming that there are no frictional losses, calculate the work that can be done by the engine. [1 mark]
Two tanks are connected by a value. One tank contains 2kg of CO2 at 77oC and 0.7 bar. The other tank has 8kg of the same gas at 27oC and 1.2 bar. The valve is opened and gases are allowed to mix while receiving energy by heat transfer from the surroundings. The final equilibrium temperature is 42oC. Using ideal gas model, determine
The final equilibrium pressure. [2 marks]
The heat transfer for the process {Cv = 0.745 kJ kg-1k-1}. [2 marks]
QUESTION THREE (20 MARKS)
(a) (i) With the help of a well labelled diagram, describe different types of
thermodynamic processes. [7 ½ marks]
(ii) Calculate the work done when 50g of iron reacts with hydrochloric acid in
a closed vessel of fixed volume [ ½ mark]
an open beaker at 25o C. [2 ½ marks]
The reaction is:
Fe(s) + 2HClaq ? FeCl2aq+ H2(g). Assumethat H2 follows the
ideal gas law {Fe = 55.8}
(b) (i) Briefly explain what we mean by “Free energy”. [5 ½ marks]
(ii) Calculate the maximum work obtained or available, expressed in kilo Joules from the oxidation of 1 mole of octane, C8H18(l), by oxygen to give CO2(g) and H2O(l) at 25oC and 1 atm.
Substance CO2 C8H18(1) H2O(g) H2Ol O2(g)
DGFo(kJ mol-1) -394.4 +17.3 -228.6 -237.2 0.0
[2 marks]
What will be the entropy change when 2 moles of an ideal gas change reversibly at 27oC from a pressure of 2 atm spheres to a pressure of 1 atmosphere? How will the value of entropy change alter if the expansion were to take place irreversibly? [2 marks]
QUESTION FOUR (20 MARKS)
(a) Explain briefly indicating reasons whether the following statements are correct or
incorrect.
Any spontaneous process is always accompanied by a decrease in free energy. [2 marks]
An adiabatic process is always isoentropic. [2 marks]
Entropy is a state function and hence does not depend on the amount of mass in the system. [2 marks]
If the same change of state from state A to State B be effected in as system in different ways, the free energy change in each case will be same provided the process are reversible. [1 mark]
(b) (i) If Ho = 0 for a reaction, then show that So = 0 for the same reaction.
[3 marks]
(ii) Derive an expression for entropy change for ideal gas associated with temperature and pressure changes. [3 marks]
(c) (i) Explain the thermodynamic efficiency. [1 mark]
(ii) Two moles of an ideal gas are allowed to expand reversibly and isothermally at 300 k from a pressure of 0.1 atm. Calculate the change in Gibbs free energy.
[1 ½ marks]
Calculate the vapour pressure of water at 90.0oC if its value at 100.0oC is 76.0cm. The mean heat of vaporization of water in the temperature range 90o and 100oC is 542 calories per gram. [1 ½ marks]
----------------------------------------------------------------------------------------------------
More Question Papers
Popular Exams
Return to Question Papers