A chemist wants to calculate the amount of heat that is absorbed by a sample of copper as it is melted. Which constant should she use?

Melting is the phase change from solid to liquid, so the chemist should use the enthalpy of fusion, ΔH_fus. Because the copper absorbs heat as it melts, the heat change is positive; therefore, the correct constant is ΔH_fus, not its negative or the enthalpy of vaporization.

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