Question

Consider the reaction $2 NO _{( g )}+ O _{2( g )} \longrightarrow 2 NO _{2( g )}$ Predict whether the reaction is spontaneous at $298 \, K . \Delta f G^{\circ}( NO )=86.69\, kJ / mol , \Delta f G^{\circ}\left( NO _2\right)$ $=51.84 \, k J / mol$

• A. Spontaneous
• B. Non-spontaneous
• C. Equilibrium
• D. Cannot predict

Answer 1

Answer: (A)

For the reaction:
$2 NO _{( g )}+ O _{2( g )} \longrightarrow 2 NO _2( g )$
$\Delta G^{\circ}=2 \Delta_f G^{\circ}\left(N O_2\right)-\left[2 \Delta_f G^{\circ}(N O)+\Delta_f G^{\circ}\left(O_2\right)\right]$
$=(2 \times 51.84)-(2 \times 86.69+0)=103.68-173-38$
$=-69.7 \,kJ / mol ; \Delta G^{\circ}$ is negative
So, the reaction is spontaneous.