CBSE Class 11 Chemistry Thermodynamics Assignment Set B

ONE MARK QUESTIONS

1. Dissolution of ammonium chloride in water is endothermic yet it is a spontaneous process. Explain

2. When will heat change at constant volume and heat change at constant pressure be equal?

3. Discuss the role of temperature in determining the spontaneity of a process.

4. Give two examples of state functions.

5. Predict the change in internal energy for an isolated system at constant volume.

TWO MARK QUESTIONS

1. Derive the relationship between Cp and Cv

2. State

i. Hess’s law of constant heat summation

ii. Second law of thermodynamics

3. Derive the relation ΔH = ΔU + Δn_gRT

4. What will be the sign of entropy change for the following changes?
a) In an isolated system, two identical gases are allowed to mix under identical conditions.
b) I₂(g) → I2(s)
c) H₂(g) + I₂(g) → 2HI(g)
d) Dissolution of sugar in water contained in a thermos flask.

5 ΔH and ΔS for the reaction Ag₂O ⇌ 2Ag + ½ O₂ are 30.56 KJ/mole and 60 J/K respectively. Calculate the temperature at which the free energy change for this reaction will be zero. Predict whether the forward reaction will be favoured above/below this T.

6 Calculate the Kc at 298 K for the reaction H₂ + I₂ ⇌ 2HI, if ΔG^of (HI) = 1.3kJ/mole

7 Differentiate between
a) heat of formation and heat of reaction
b) heat of hydration and heat of solution

8 Calculate heat change at constant pressure if heat change at constant volume for the reaction NH₂CN(g) + 3/2 O₂(g) → N2(g) + CO₂(g) + H₂O(l) at 298K is -742 kJ/mole

9 What would be the work done when the pressure of 2 moles of an ideal gas is changed from 2 bar to 5 bar isothermally and reversibly at 25^oC ?

THREE MARK QUESTIONS

1 Define
(i) Molar heat capacity (ii) Enthalpy of a reaction (iii) Residual entropy

2 Comment on the following statements
(i) An exothermic reaction is always thermodynamically spontaneous.
(ii) The entropy of a substance increases when going from liquid state to vapour state at any temperature.
(iii) A reaction with ΔG0 >0 always has an equilibrium constant greater than one

3 (i) For the equilibrium PCl₅ ⇌ PCl₃ + Cl₂ at 25 ⁰C, K = 1.8 x 10^-7. Calculate ΔG^o of reaction
(ii) For the reaction 2NO (g) + O₂(g) ⇌ 2NO₂(g), calculate the ΔG at 600 K if enthalpy and entropy changes are –110kJ/mole and 150 J/Kmole

4 For the synthesis of NH₃ ,N₂(g) + 3H₂(g)⇌ 2NH₃(g), calculate Kp at 300K if ΔH^of of

5 NH₃ as -46.2 kJ/mole and ΔS^o for the reaction is 198.3 J/Kmole.
(i) The ΔH_vap of water at 100^oC is 41kJ/mole. Calculate the internal energy change.
(ii) What is the work done on a gas when 10 lt of the gas is compressed to 4.5 lt under a constant pressure of 103kPa?

6 Calculate the ΔH⁰f of benzene if ΔH_comb of benzene, carbon and hydrogen are 3267, 393 and 286 kJ/mole respectively.

7 The mean bond enthalpies of N≡N and H-H are 946 and 436 kJ/mole respectively. If heat of formation of ammonia is -46kJ/mole, calculate the mean BE of N-H bonds in ammonia.

8 (i) Calculate the entropy change in surroundings when 36 g of water is formed under standard conditions. ΔH⁰f of water = -286kJ/mole
(ii) Calculate the work done when 2.5 moles of an ideal gas at 300K is isothermally and reversibly compressed from a volume of 5m3 to a volume of 2 m³