State the second law of thermodynamics.

The second law of thermodynamics can be expressed in terms of entropy. It can be stated as “the entropy of an isolated system increases during a spontaneous process”. The total entropy change ( ∆ S total ) for the system and the surroundings of a spontaneous process is given by, ∆ S total = ∆ S system + ∆ S surrounding > 0 When a system is in equilibrium, the entropy is maximum and the change in entropy, ∆ S = 0 . Hence, entropy of a spontaneous process increases till it reaches a maximum and at equilibrium the change in entropy is zero.

The work done in ergs for the reversible expansion of one mole of an ideal gas from a volume of 10 litres to 20 litres at 25 ° C is

298 × 10 7 × 8 . 31 × 2 . 303 log 2 .

2 . 303 × 298 × 0 . 082 log 2 .

2 . 303 × 298 × 0 . 082 log 0 . 5 .

8 . 31 × 10 7 × 298 × 2 . 303 log 0 . 5 .

For a reaction taking place in a container in equilibrium with its surroundings, the effect of temperature on its equilibrium constant K in terms of change in entropy is described by:

with increase in temperature, the value of K for exothermic reaction decreases because favourable change in entropy of the surroundings decreases.

with increase in temperature, the value of K for exothermic reaction decreases because the entropy change of the system is positive.

with increase in temperature, the value of K for endothermic reaction increases because the entropy change of the system is negative.

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For two moles of an ideal gas-

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Important Questions on Thermodynamics

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 53

The heat of combustion of ethanol at a constant pressure and at

298 K

is found to be

- Q kJ

{mol}^{- 1} .

Hence, the heat of combustion of ethanol at the same temperature and a constant volume will be:

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 54

${NH}_{3}_{(g)} ⟶ {NH}_{2 (g)} + H_{(g)}$

${NH}_{2 (g)} ⟶ {NH}_{(g)} + H_{(g)}$

${NH}_{(g)} ⟶ N_{(g)} + H_{(g)}$

The enthalpy changes for the above reactions:

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 55

How much heat is absorbed in the complete reaction of

3.00

g of

{SiO}_{2}

with excess carbon in the reaction below?

{SiO}_{2 (g)} + 3 C_{(S)} ⟶ {SiC}_{(S)} + 2 {CO}_{(g)}; ΔH ° = + 624.7 kJ

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 56

Estimate the temperature at which $\Delta G=0$ for the following reaction:
(Given:

ΔH = - 176 kJ

and

ΔS = - 284.5 J / K

). Caution: Beware of units.

{NH}_{3}_{(g)} + {HCl}_{(g)} ⟶ {NH}_{4} {Cl}_{(s)}

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 57

A particular chemical reaction is characterised by

{ΔH}_{rxn} = + 250 kJ / mol

. Which of the following statements is/are true concerning this reaction?
I. Heat is liberated to the surroundings.
II. The reaction is endothermic.
III. The total heat content of the products is lower than that of the reactants.

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 58

Of the following composition, for the mixture of

H_{2 (g)}

and

N_{2 (g)}

, which gives rise to maximum entropy of mixing?

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 60

Which of the following processes is/are accompanied by an increase in the entropy of the system?
(i) Water freezes
(ii) lodine sublimes at room temperature
(iii) A building is constructed from bricks and mortar
(iv) A partition is removed to allow two gases to mix

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Alpha Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>Exercise-4>Q 61

A reference book lists the heat of formation of

{NH}_{3 (g)}

to be

- 46 kJ {mol}^{- 1} .

The

ΔH

(in

kJ {mol}^{- 1}

) of the reaction:

2 {NH}_{3} (g) ⟶ N_{2} (g) + 3 H_{2} (g)

For two moles of an ideal gas-

Important Questions on Thermodynamics

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