Which of the following correctly represents an exothermic reaction equation?

• A. A + B → C + D + heat
• B. A + B + heat → C + D
• C. A + B → C + D (energy absorbed)
• D. A + B → C + D (ΔH > 0)

Answer: (A)

Verified step by step guidance

1. Understand the difference between exothermic and endothermic reactions: Exothermic reactions release heat to the surroundings, while endothermic reactions absorb heat from the surroundings.
2. Recall that in an exothermic reaction, heat is a product because energy is released. This means the reaction equation should show heat on the product side.
3. Analyze the given options to identify which one shows heat being produced (on the right side of the equation) rather than consumed (on the left side).
4. Recognize that if heat is written as a reactant (on the left side), the reaction is endothermic, meaning it requires energy input.
5. Note that the sign of enthalpy change (ΔH) helps identify the reaction type: ΔH < 0 indicates exothermic (heat released), and ΔH > 0 indicates endothermic (heat absorbed). Therefore, the correct exothermic equation will have heat as a product and ΔH < 0.