In the context of enthalpy of formation, what does it mean when the enthalpy change (ΔH) for a reaction is negative?

• A. The reaction releases energy to the surroundings and is exothermic.
• B. The reaction occurs only at high temperatures.
• C. The reaction does not involve any energy change.
• D. The reaction absorbs energy from the surroundings and is endothermic.

Answer: (A)

Verified step by step guidance

1. Understand that the enthalpy change (\$\Delta H\$) for a reaction represents the heat absorbed or released during the reaction at constant pressure.
2. Recognize that a negative value of \$\Delta H\$ means the system is losing heat to the surroundings.
3. Recall that when heat is released to the surroundings, the reaction is called exothermic.
4. Contrast this with a positive \$\Delta H\$, which indicates heat absorption and an endothermic reaction.
5. Therefore, a negative \$\Delta H\$ means the reaction releases energy to the surroundings and is exothermic.