Which statement best describes exothermic and endothermic reactions?

Which statement best describes exothermic and endothermic reactions?

• A. Exothermic releases energy to surroundings (ΔH negative); endothermic absorbs energy (ΔH positive).
• B. Endothermic releases energy to surroundings (ΔH negative).
• C. ΔH is always positive for exothermic reactions.
• D. There is no energy change in exothermic reactions.

Answer: (A)

Energy change during reactions distinguishes exothermic and endothermic processes. In an exothermic reaction, energy is released to the surroundings, so the enthalpy change ΔH for the reaction is negative. In an endothermic reaction, energy is absorbed from the surroundings, so ΔH is positive. The statement that best describes both cases is that exothermic reactions release energy to the surroundings (ΔH negative) and endothermic reactions absorb energy from the surroundings (ΔH positive). This aligns with real examples: burning fuel warms the surroundings, while dissolving some salts in water can feel cold as heat is absorbed. The other options misstate the direction of energy flow or the sign of ΔH, or claim no energy change at all, which isn’t true for these processes.

Energy change during reactions distinguishes exothermic and endothermic processes. In an exothermic reaction, energy is released to the surroundings, so the enthalpy change ΔH for the reaction is negative. In an endothermic reaction, energy is absorbed from the surroundings, so ΔH is positive. The statement that best describes both cases is that exothermic reactions release energy to the surroundings (ΔH negative) and endothermic reactions absorb energy from the surroundings (ΔH positive). This aligns with real examples: burning fuel warms the surroundings, while dissolving some salts in water can feel cold as heat is absorbed. The other options misstate the direction of energy flow or the sign of ΔH, or claim no energy change at all, which isn’t true for these processes.