Question

In Haber's process of manufacturing of ammonia :

N2(g) + 3H2(g) $\longrightarrow$ 2NH3(g) ; $H_{25^{0}C}^{0}$= –92.2 Kj

Molecule N2(g) H2(g) NH3(g)

CP JK-1mol–1 29.1 28.8 35.1

If CP is independent of temperature, then reaction at 100⁰C as compared to that of 25⁰C will be :

• A. More endothermic
• B. Less endothermic
• C. More exothermic
• D. Less exothermic

Answer 1

Answer: (C)

More exothermic

Answer 2

$\Delta$H⁰ = –92.2

$\Delta$CP = 2CP (NH3, g) – CP (N2, g) – 3CP (H2) = 2 × 35.1 – 29.1 – 3 × 28.8

= 70.2 – 29.1 – 86.4 = – 45.3 J/K

$\Delta$H⁰100⁰C = $\Delta$H⁰25⁰C + $\Delta$CP ($\Delta$T) = – 92.2 – $\frac{45.3 \times 75}{1000}$

$\Delta$H⁰100⁰C = – 92.2 – 1.3975 = – 95.6 kJ/mole

Then, reaction at 100⁰C as compared to that at 25⁰C will be more exothermic.