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# For the reaction between $CO_2$ and graphite $CO_2(g) + C(s) \longrightarrow 2CO(g)$ $\Delta H = +170.0 kJ$ and $\Delta S = 170 JK^{-1}$. The reaction is spontaneous at

(a) 298 K
(b) 500 K
(c) 900 K
(d) 1200 K
Can you answer this question?

$\Delta H$ = 170,000 J and $\Delta S = 170 JK^{-1}$
When, $\Delta G = 0$ (equilibrium)
At equilibrium, $T\Delta S = \Delta H$
$T = \frac{\Delta H}{\Delta S} = \frac{170,000}{170}$ = 1000 K
For the reaction to be spontaneous T must be > 1000 K.
answered Feb 24, 2014