For the reaction at 298 K, 2A + B → C, ΔH = ...

NCERT Class XI Chemistry Thermodynamics Solutions

Question : 17 of 22

Marks: +1, -0

For the reaction at 298 K, 2A + B → C, ΔH = 400

\text{kJ mol}^{-1}

and ΔS = 0.2

\text{kJ K}^{-1}\text{ mol}^{-1}

. At what temperature will the reaction become spontaneous considering ΔH and ΔS to be constant over the temperature range.

Solution:

According to Gibbs Helmholtz equation, ΔG = ΔH – TΔS.

At equilibrium, ΔG = 0

∴ T =

\frac{\Delta H}{\Delta S}

\frac{400}{0.2}

\frac{4000}{2}

= 2000 K

Thus, the reaction will be spontaneous at temperature above 2000 K.

[Since Above 2000 K, ΔG = –ve]

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