Question

Select all of the following equations that represent an exothermic reaction.

A. C + 2S → CS₂, ΔH = ₂7,550 cal
B. NH ₃(g) + 1₂.0 kcal → ½N ₂(g) + 3/2 H ₂(g)
C. CH₄ + 2O ₂ → CO ₂ + 2H ₂O + 1,800 cal
D. 2H ₂O → 2H_₂ + O ₂, ΔH = +58 kcal
E. C (graphite) → C (diamond), ΔH = - 0.45 kcal

Answer 1

The equations representing exothermic reactions are A (C + 2S → CS₂, ΔH = -27,550 cal), C (CH₄ + 2O₂ → CO₂ + 2H₂O + 1,800 cal), and E (C (graphite) → C (diamond), ΔH = - 0.45 kcal), as they all release energy indicating a negative ΔH value.

Step-by-step explanation:

To determine whether each chemical reaction is exothermic or endothermic, we need to look at the energy change, represented by ΔH. An exothermic reaction releases heat, resulting in a negative ΔH, whereas an endothermic reaction absorbs heat, indicated by a positive ΔH.

• A. C + 2S → CS₂, ΔH = -27,550 cal is exothermic because energy is released (negative ΔH).
• B. NH₃(g) + 12.0 kcal → ½N₂(g) + ⅔H₂(g) is endothermic because energy is absorbed (positive ΔH).
• C. CH₄ + 2O₂ → CO₂ + 2H₂O + 1,800 cal is exothermic as it releases heat.
• D. 2H₂O → 2H₂ + O₂, ΔH = +58 kcal is endothermic since heat is absorbed.
• E. C (graphite) → C (diamond), ΔH = - 0.45 kcal is exothermic as it releases a small amount of energy.

Therefore, the exothermic reactions are A, C, and E.