Comment on the thermodynamic stability of $NO_{(g)}$,given:
$\frac{1}{2} N_{2(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{(g)}; \Delta_r H^{\ominus} = 90 \, kJ \, mol^{-1}$
$NO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{2(g)}; \Delta_r H^{\ominus} = -74 \, kJ \, mol^{-1}$
$\frac{1}{2} N_{2(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{(g)}; \Delta_r H^{\ominus} = 90 \, kJ \, mol^{-1}$
$NO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{2(g)}; \Delta_r H^{\ominus} = -74 \, kJ \, mol^{-1}$
(N/A) The positive value of $\Delta_r H^{\ominus} = 90 \, kJ \, mol^{-1}$ indicates that heat is absorbed during the formation of $NO_{(g)}$ from its elements.
This means that $NO_{(g)}$ has higher energy than the reactants ($N_{2(g)}$ and $O_{2(g)}$),making it thermodynamically unstable.
Conversely,the negative value of $\Delta_r H^{\ominus} = -74 \, kJ \, mol^{-1}$ for the reaction $NO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{2(g)}$ indicates that heat is evolved,leading to a more stable product $NO_{2(g)}$.
Therefore,$NO_{(g)}$ is thermodynamically unstable and tends to convert into $NO_{2(g)}$.
This means that $NO_{(g)}$ has higher energy than the reactants ($N_{2(g)}$ and $O_{2(g)}$),making it thermodynamically unstable.
Conversely,the negative value of $\Delta_r H^{\ominus} = -74 \, kJ \, mol^{-1}$ for the reaction $NO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{2(g)}$ indicates that heat is evolved,leading to a more stable product $NO_{2(g)}$.
Therefore,$NO_{(g)}$ is thermodynamically unstable and tends to convert into $NO_{2(g)}$.
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