In the Ellingham diagram ( vs ), the plot for the reaction exhibits a unique characteristic compared — Metallurgy and Isolation of Elements Chemistry Question
Question
In the Ellingham diagram ($\Delta G^\circ$ vs $T$), the plot for the reaction $2C_{(s)} + O_{2(g)} \rightarrow 2CO_{(g)}$ exhibits a unique characteristic compared to virtually all metal oxidation curves. What is this characteristic and its thermodynamic origin?
Answer: C
💡 Solution & Explanation
For $2C_{(s)} + O_{2(g)} \rightarrow 2CO_{(g)}$, 1 mole of $O_2$ gas reacts to form 2 moles of $CO$ gas. Since $\Delta n_g > 0$, the entropy change $\Delta S$ is positive. Using $\Delta G = \Delta H - T\Delta S$, a positive $\Delta S$ makes the slope ($-\Delta S$) negative, causing the line to plunge downwards as $T$ increases.
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