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Magnesium carbonate decomposes: MgCO₃(s) → MgO(s) + CO₂(g), with Δ H° = +117.6 kJ/mol and Δ S° =…

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Magnesium carbonate decomposes: $\text{MgCO}_3(s) \rightarrow \text{MgO}(s) + \text{CO}_2(g)$ , with $\Delta H^\circ = +117.6\ \text{kJ/mol}$ and $\Delta S^\circ = +175.0\ \text{J/(K mol)}$ . Above what temperature is the decomposition spontaneous? Is it spontaneous at $298\ \text{K}$ ?

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Gibbs energy: $G = H - TS$ , and at constant temperature $\Delta G = \Delta H - T\Delta S$ . $\Delta G < 0$ : spontaneous; $\Delta G = 0$ : equilibrium; $\Delta G > 0$ : not spontaneous. When $\Delta H$ and $\Delta S$ have the same sign, $\Delta G$ changes sign at $T = \Delta H/\Delta S$ . Put $\Delta S$ in kJ/(K mol), or $\Delta H$ in J/mol, before combining them.

The worked solution

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← For N₂(g) + 3H₂(g) → 2NH₃(g), Δ H° = -92.4 kJ/mol and Δ S° = -198.7 J/(K mol).Four reactions have these signs. (a) Δ H < 0, Δ S > 0. →

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Magnesium carbonate decomposes: MgCO₃(s) → MgO(s) + CO₂(g), with Δ H° = +117.6 kJ/mol and Δ S° =…

The worked solution

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