HARD

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Work done by the system in isothermal reversible process is: $w_{r e v} = - 2.303 n R T \log \frac{V_{2}}{V_{1}}$ . Also in case of adiabatic reversible process work done by the system is given by: $w_{r e v} = \frac{n R}{γ - 1} [T_{2} - T_{1}]$ . During expansion disorder increases and the increase in disorder is expressed in terms of change in entropy $Δ S = \frac{Δ H}{T}$ . Both entropy and enthalpy changes obtained for a process were taken as a measure of spontaneity of process but finally it was recommended that decrease in free energy is responsible for spontaneity and $Δ H - T Δ S$ .

The heat of vaporization and heat of fusion of $H_{2} O$ are 540 cal/g and 80 cal/g. The ratio of $\frac{Δ S_{v a p}}{Δ S_{f u s i o n}}$ for water is:

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Important Questions on Thermodynamics

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

Using the Gibbs change,

∆ G^{o} = + 63.3 k J,

for the following reaction,

A g_{2} C O_{3} (g) ⇌ 2 A g^{+} (a q) + C O_{3}^{2 -} (a q)

the

K_{s p}

A g_{2} C O_{3} (s)

in water at

25^{o} C

(R = 8.314 J K^{- 1} m o l^{- 1})

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

In which case change in entropy is negative?

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For the reaction:

X_{2} {O_{4}}_{(l)} \to 2 X {O_{2}}_{(g)}

∆ U = 2 .1 kcal, ∆ S = 20 cal K^{- 1}

300 K

Hence,

∆ G

is:

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

If for a certain reaction

Δ_{r} H

30 {kJmol}^{- 1}

450 K,

the value of

Δ_{r} S

(in

{JK}^{- 1} {mol}^{- 1}

) for which the same reaction will be spontaneous at the same temperature is

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

The process with negative entropy change is:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For the reaction,

2 Cl (g) \to {Cl}_{2} (g)

, the correct option is

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

A process will be spontaneous at all temperatures if:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For a reaction to be spontaneous at all the temperatures, what are the required thermodynamic quantities?

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For spontaneous polymerisation, which of the following is (are) correct?

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

Which of the following can help predict the rate of a reaction if the standard Gibbs free energy of reaction

(Δ G^{0})

is known?

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

Which of the following show an increase in entropy?

I. Boiling of water

II. Melting of ice

III. Freezing of water

IV. Formation of hydrogen gas from water

HARD

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

One mole of an ideal gas at

300 K

in thermal contact with its surroundings expands isothermally from

1.0 L

2.0 L

against a constant pressure of

3.0 atm

. In this process, the change in entropy of the surroundings

(∆ S_{s u r r})

J K^{- 1}

is:

(1 L atm = 101.3 J)

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

When the heat of a reaction at constant pressure is

- 25 \times 10^{- 3} cal

and entropy change for the reaction is

7.4 cal {deg}^{- 1}

, it is predicted that the reaction at

25^{0} C

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

The true statement amongst the following is:

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For the reaction.

2 H_{2} (g) + O_{2} {(g)}_{} ⟶ 2 H_{2} O {(g)}_{}, at 300 K, ΔG

and

ΔH

of water are

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

and

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

, respectively. Then calculate the value of change in entropy for the given reaction.

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For the following reaction

${Fe}_{2} O_{3 (s)} + 3 {CO}_{(g)} ⟶ 2 {Fe}_{(s)} + 3 {CO}_{2 (g)} ΔH ° = - 29.8 kJ$ and $ΔS ° = 15 {JK}^{- 1}$ . What is the value of ${ΔS}_{(total)}$ at $298 K$ ?

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For a reaction

ΔH = - 30 kJ

and

ΔS = - 45 J K^{- 1},

at what temperature reaction changes from spontaneous to non-spontaneous ?

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

For a given reaction,

Δ H = 35.5 k J m o l^{- 1}

and

Δ S = 83.6 J K^{- 1} m o l^{- 1} .

The reaction is spontaneous at : (Assume that

Δ H

and

Δ S

do not vary with temperature)

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

A process has

Δ H = 200 J m o l^{- 1}

and

Δ S = 40 J K^{- 1} m o l^{- 1} .

Out of the values given below choose the minimum temperature above which the process will be spontaneous:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Spontaneity

Standard entropies of

X_{2}, Y_{2}

and

{XY}_{3}

are

60, 30

and

50

{JK}^{- 1} {mol}^{- 1}

respectively. For the reaction

\frac{1}{2} X_{2} + \frac{3}{2} Y_{2} ⇌ {XY}_{3},

ΔH = - 30 kJ

to be at equilibrium, the temperature should be:

Important Questions on Thermodynamics

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