Delhi University
Chemistry Paper VI Physical Chemistry Previous Year Question Paper Year 2005 : IInd Year
Q. 1. Answer the following:
(i) How would the energy of an ideal gas change if it is made to expand into vacuum at constant temperature ?
(ii) What is the relation between AH and AE for a reaction involving only condensed phases ?
(iii) Which one of the following properties is an intensive variable:
Internal energy, volume, chemical potential Entropy?
(iv) What is the change in the value of a state function of a system undergoing a cyclic process ?
(v) Under what conditions is ΔG=ΔA?
(vj) Correct the expression : Cp m - Cv m = nR.
(vii) In a reversible process, what is the relationship between internal pressure of a gaseous system and external pressure on it ?
Answer :
Q. 2. (a) Show that for an ideal gas undergoing reversible adiabatic changes
(i) PV y= Constant
(ii) TV y-1= Constant
(b) Calculate W, q, ΔE and ΔH when 2 moles of an ideal gas at 300 K are compressed from 1 atm to 10 atm isothermally and reversibly. What would be the values of the above quantities if the changes were irreversible and carried out against a constant external pressure of 10 atm.
Answer :
Q.3. (a) Derive the relation
Image no.3
Integrate the above equation when Cp values are temperature dependent and ΔCp is given by
ΔC p = Aα + ΔβT + ΔγT2 +…………
(b) The reaction of Cyanamide NH2 CN (S) with oxygen was seen in a bomb calorimeter and ΔE was found to be - 742.7 kj/ mol of NH2 CN (S) at 298 K. Calculate ΔH298 for the reaction
NH2CH(S)+3/2O2(g)—>N2((g) + C02(K) + H20(ℓ)
(c ) If P = f(V,T)show that :
Image no.4
Answer :
Q.4 (a) Explain the term chemical potential and show that :
Image no.5
(b) Show that the decrease in free energy AG is a measure of net useful work under conditions of constant pressure and temperature.
(c ) During a reversible isothermal compression of one of an ideal gas, its pressure increases from 1 atm to 100 atm at a temperature of 27°C. Calculate the entropy change and the free energy change.
Answer :
Q.5. (a) Derive the relation dluKP =AH1
Image no.6
(b) Taking the reaction
so2(g) + ½ O2 (g)=SO3(g)
discuss the effect of an inert gas on the equilibrium.
(c ) The value of K p for the reaction
½ H2(g) + ½ l2(g)=HI(g)
is 8.32 at 600°C and 1 atm pressure. Calculate K p, K c and K x for :-
(i) 2HI(g)=H2(g)=l2(g)
(ii) H2(g) + I2(g)=2HI(g)
Answer :
Q. 6, (a) What do you understand by molal elevation constant of a solvent ? Assuming the clausius-clapeyron equation, derive the expression for the molal elevation constant of a solvent Discuss its
utility.
(b) A solution containing 0.5126 g of naphthalene (M.wt = 128,17) in 50.0 g of carbon tetrachloride yields a boiling point elevation of 0.402°C, while a solution of 0.6126 g of an unknown solute in the same weight of solvent gives a boiling point elevation of 0.647°C. Find the molecular weight of the unknown solute.
Answer :