Which of the following best describes the enthalpy change (ΔH) associated with an endothermic reaction?

• A. ΔH is zero because there is no heat exchange.
• B. ΔH is positive because the system absorbs heat from the surroundings.
• C. ΔH is negative because the system releases heat to the surroundings.
• D. ΔH can be either positive or negative depending on the temperature.

Answer: (B)

Verified step by step guidance

1. Understand that enthalpy change (\$\Delta H\$) represents the heat absorbed or released by a system at constant pressure during a chemical reaction.
2. Recall that an endothermic reaction is one in which the system absorbs heat from the surroundings, meaning energy flows into the system.
3. Recognize that when heat is absorbed by the system, the enthalpy change (\$\Delta H\$) is positive, indicating an increase in the system's enthalpy.
4. Contrast this with exothermic reactions, where heat is released to the surroundings and \$\Delta H\$ is negative.
5. Conclude that for an endothermic reaction, the best description is that \$\Delta H\$ is positive because the system absorbs heat from the surroundings.