A scientist needs to calculate the amount of heat released when a sample of melted iron freezes. Which constant should be used?

Freezing is the reverse of melting (fusion). Melting absorbs heat and has enthalpy change ΔHfus, so freezing releases the same amount of heat with the opposite sign: –ΔHfus. Therefore, use –ΔHfus, choice C.

AI-written and checked against the verified answer.