Given that the standard molar enthalpies of formation of NO(g) and NO₂(g) are, respectively, 90.3 kJ mol⁻¹ and 33.2 kJ mol⁻¹, the enthalpy change for the reaction 2NO(g) + O₂(g) → 2NO₂(g) is

(c) -114.2 kJ. Explanation: ΔH = 2ΔHf(NO₂) − 2ΔHf(NO) = 2(33.2) − 2(90.3) = −114.2 kJ (c).

Given that the standard molar enthalpies of formation of NO(g) and NO₂(g) are, respectively, 90.3 kJ mol⁻¹… · ABC26PH0599

Subject: Physical Chemistry · Chapter: Thermodynamics · Topic: Thermodynamics – General · Exam: GATE 2005-2021 · Marks: 2 · Difficulty: Easy

Given that the standard molar enthalpies of formation of $\mathrm{NO(g)}$ and $\mathrm{NO_2(g)}$ are, respectively, $90.3\ \mathrm{kJ\,mol^{-1}}$ and $33.2\ \mathrm{kJ\,mol^{-1}}$, the enthalpy change for the reaction $2\mathrm{NO(g)} + \mathrm{O_2(g)} \rightarrow 2\mathrm{NO_2(g)}$ is

(a)$16.6\ \mathrm{kJ}$

(b)$-57.1\ \mathrm{kJ}$

(c)$-114.2\ \mathrm{kJ}$

(d)$57.1\ \mathrm{kJ}$

Answer

Answer: C ✓ checked by 4AB · confidence high

The source book printed B; on checking, C is correct — see the explanation.

Explanation

ΔH = 2ΔH_f(NO₂) − 2ΔH_f(NO) = 2(33.2) − 2(90.3) = −114.2 kJ (c).

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