Study the following thermochemical equations:<br><br><br>The correct order of enthalpies of formatio — Thermodynamics and Thermochemistry Chemistry Question
Question
Study the following thermochemical equations:<br>$\text{A} \to \text{B}; \Delta H = +100\text{ kcal}$<br>$\text{B} \to \text{C}; \Delta H = -80\text{ kcal}$<br>The correct order of enthalpies of formation of A, B and C is
Answer: B
💡 Solution & Explanation
Reaction 1 tells us $H_B - H_A = 100 \implies H_B > H_A$. Reaction 2 tells us $H_C - H_B = -80 \implies H_B > H_C$. Adding both tells us $H_C - H_A = 20 \implies H_C > H_A$. Ordering them: $H_A < H_C < H_B$.
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