# NIOS Spontaneity of Chemical Reactions Intext Questions With Answer

### National Institute of Open Schooling (NIOS)

Sr. Secondary, Module-4

Lession-10: NIOS Spontaneity of Chemical Reactions Intext Questions With Answer

## INTEXT QUESTIONS 10.1

### 1. The enthalpy change for the transition of ice to liquid water at 273 K is 6.02 kJ mol^{–1}. Calculate the entropy change for the process.

**Answer:**We know that Gibbs Helmholtz equation-

ΔG = ΔH − TΔS

where, ΔH is Change in enthalpy

ΔS is Change in entropy

T is Temperature in kelvin (K)

As ΔG = 0

so from Gibbs Helmholtz equation, ΔH = TΔS

or, ΔS = ΔH/T

or, ΔS = 6.02 x 10

^{3}Jmol

^{−1}/273K

or, ΔS = 22.051Jmol

^{−1}or, Entropy change (ΔS) for given transition is 22.051Jmol

^{−1}

### 2. Arrange the following systems in the order of increasing randomness,

(i) 1 mol of gas A

(ii) 1 mol of solid A

(iii) 1 mol of liquid A

**Answer:**Order of increasing randomness-

(ii) 1 mol of solid A < (iii) 1 mol of liquid A < (i) 1 mol of gas A

### 3. Indicate whether you would expect the entropy of the system to increase or decrease

(a) 2SO_{2}(g) + O_{2}(g) → 2SO_{3}(g)

(b) N_{2}(g) + 3H_{2}(g) → 2NH_{3}(g)

(c) O_{2}(g) → 2O(g)

**Answer:**a. Decreased b. Decreases c. Increased.

## INTEXT QUESTIONS 10.2

### 1. Determine whether the following reaction

CCl_{4} (l) + H_{2} (g) → HCl (g) +CHCl_{3} (l)

is spontaneous at 298 K if ΔrH = 91.35 kJ mol–1 and Δ_{r}S = 41.5 JK–1 mol^{–1} for this reaction.

**Answer:**ΔG = –103.7 kJ. Therefore, the reaction is spontaneous.

### 2. Which of the following conditions would predict a process that is always spontaneous?

**(i) ΔH > 0, Δ S > 0**

(ii) Δ H > 0, Δ S < 0

(iii) Δ H < 0, Δ S > 0

(iv) Δ H < 0, Δ S < 0

(ii) Δ H > 0, Δ S < 0

(iii) Δ H < 0, Δ S > 0

(iv) Δ H < 0, Δ S < 0

**Answer:**iii. Δ H < 0, Δ S > 0

## INTEXT QUESTIONS 10.3

### 1. What is the relationship between the standard Gibbs energy change and the equilibrium constant of the reaction

**Answer:**ΔG

^{o}= – RT lnK

Or, ΔG

^{o}= – 2.303 RT log K

### 2. The standard Gibbs energy change for the reaction

CO (g) + 2H_{2}(g) ⎯⎯→ CH_{3}OH (l)

at 298 K is – 24.8 kJ mol^{−1}. What is the value of the equilibrium constant at298 K

**Answer:**Temperature(T) = 298K

Standard Gibbs energy change(ΔG

^{o}) = −24.8KJ

Gas constant(R) = 0.008314kJmol

^{−1}K

^{−1}

Equilibrium constant(K) = ?

ΔG

^{o}= −RTInK

Or, lnK = ΔG

^{o}/ − RT

Putting all the values of ΔG

^{o}, R and T we get-

logK = −24.8 / (−298 × 0.008314 × 2.303)

or, logK = 4.346418

or, K = 22203.20

or, K = 2.2 × 10

^{4}