When a chemical process is reversed, how do the magnitude and sign of the enthalpy change (ΔH) compare to the original process?

• A. The magnitude increases, and the sign is reversed.
• B. Both the magnitude and the sign remain the same.
• C. The magnitude decreases, but the sign remains the same.
• D. The magnitude remains the same, but the sign is reversed.

Answer: (D)

Verified step by step guidance

1. Understand that enthalpy change (\$\Delta H\$) is a state function, meaning it depends only on the initial and final states of a process, not on the path taken.
2. Recognize that when a chemical process is reversed, the initial and final states swap places, so the enthalpy change for the reverse process must have the same magnitude but opposite sign.
3. Express this relationship mathematically as: \$\Delta H_{reverse} = -\Delta H_{forward}\$.
4. Note that the magnitude (absolute value) of \$\Delta H\$ remains unchanged because the energy difference between the states is the same regardless of direction.
5. Conclude that the correct description is: the magnitude remains the same, but the sign of \$\Delta H\$ is reversed when the process is reversed.