Standard enthalpy and standard entropy changes for the oxidation of ammonia at $298 \mathrm{~K}$ are $-382…

Standard enthalpy and standard entropy changes for the oxidation of ammonia at $298 \mathrm{~K}$ are $-382.64 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and -145.6 $\mathrm{JK}^{-1} \mathrm{~mol}^{-1}$, respectively. Standard Gibbs energy change for the same reaction at $298 \mathrm{~K}$ is:
  1. $-221.1 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  2. $-339.3 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  3. $-439.3 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  4. $-523.2 \mathrm{~kJ} \mathrm{~mol}^{-1}$

Solution

$\Delta \mathrm{G}=\Delta \mathrm{H}-\mathrm{T} \Delta \mathrm{S}=-382.64-298 \left(\frac{-145.6}{1000}\right)$ $\begin{aligned} & =-382.64+43.38 \\ & =-339.3 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}$ Related Theory Free energy is an extensive quantity, but the standard free energy is an intensive quantity.

Asked in: NEET 2004

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