Engineering Chemistry S Datta

102 ENGINEERING CHEMISTRY
11. Show that entropy change for an irreversible isothermal expansion of an ideal gas is positive.
12. Entropy change for the mixture of gases can be represented by
– ∆S mix
= – nR Σ x i
ln x i
where x i
= mole fraction of gas.
13. (a) What do you mean by work function (A)?
(b) What do you mean by free energy (G)?
(c) What is the relationship between free energy and useful work?
(d) What do you mean by standard free energy change?
14. (a) State Hess’s law.
(b) Mention the applications of Hess’s law.
(c) Explain the terms (i) Heat of reaction, (ii) Heat of combustion, (iii) Heat of neutralisation,
(iv) Heat of formation, (v) Heat of solution, (vi) Heat of fusion, (vii) Heat of vaporisation,
(viii) Heat of sublimation.
15. How can you determine the bond energy and lattice energy with the help of Hess’s law?
16. (a) Derive Gibbs-Helmholtz equation.
(b) Give the significance of Gibbs-Helmholtz equation.
17. Derive Clausius-Clapeyron equation.
18. (a) How can you determine spontaneity of changes of a system?
(b) What do you mean by chemical potential (µ)?
(c) Show that chemical potential does not change during phase transfer of a compound.
19. Derive Maxwell’s relation and state its usefulness.
20. Derive an expression for chemical potential at a temperature T in terms of P.
21. Derive Gibbs-Duhem relations.
22. What do you mean by Van’t Hoff reaction isotherm? Derive an expression for the reaction isotherm
of the general reaction aA + bB + ... lL + mM + ... .
Long Questions
1. When ice melts at 0°C, the latent heat of fusion is 80 cals. g –1 . The density of ice is 0.82 and of
water of unity. Calculate ∆E, ∆H, q and w per mole.
(1440.1 cals; 1440 cals; 1440; cals; – 4.01 × 10 6 ergs)
2. Calculate ∆E and ∆H if 10 litres of helium at N.T.P. are heated inside a gas cylinder to 100°C
assuming it to behave ideally and having C v
= 3 2 R .
[Ans. 133.8; 223.1 cals]
3. A system performs 8.36 × 10 9 ergs work after absorbing 990 cals. heat from the surrounding.
Find the internal energy change of the system.
[Ans. 790 cals]
4. The volume of a 45 g nitrogen gas is expanded from 5 litre to 10 litre at 25°C isothermally and
reversibly. Considering the gas to be an ideal find out the work obtained in this case.
[Ans. 2.788 × 10 7 ergs]
5. During isothermal reversible expression of 4 g of helium gas at 27°C the pressure reduces from
10 atm to 1 atm. Calculate the work done in calories. Consider the gas to behave like an ideal.
[Ans. 1381.8 cals]
6. The heats of formation of CO 2
from diamond and graphite are – 94500 and – 94050 cal, respectively.
What is the enthalpy change in the transformation of diamond to graphite? [Ans. – 450 cal]
7. Calculate the heat of oxidation of ethyl alcohol to carbon dioxide, when the heats of formation of
carbon dioxide and liquid water are given as – 94.05 and – 68.32 Kcal. The heat of formation of
ethyl alcohol is – 66.4 Kcal.
[Ans. 326.6 Kcal]