# 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 Î”G=Î”A?

(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, Î”E and Î”H 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 Î”Cp is given by

Î”C p = AÎ± + Î”Î²T + Î”Î³T2 +…………

**(b) **The reaction of Cyanamide NH2 CN (S) with oxygen was seen in a bomb calorimeter and Î”E was found to be – 742.7 kj/ mol of NH2 CN (S) at 298 K. Calculate Î”H298 for the reaction

NH2CH(S)+3/2O2(g)—>N2((g) + C02(K) + H20(â„“)

**(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 27Â°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) + Â½ O2 (g)=SO3(g)

discuss the effect of an inert gas on the equilibrium.

**(c )** The value of K p for the reaction

Â½ H2(g) + Â½ l2(g)=HI(g)

is 8.32 at 600Â°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 0.402Â°C, while a solution of 0.6126 g of an unknown solute in the same weight of solvent gives a boiling point elevation of 0.647Â°C. Find the molecular weight of the unknown solute.

**Answer : **