PPT Slide

• When one mole of substance melts, the enthalpy change is the heat of fusion (_H fus ):

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• When one mole of a substance vaporizes, the enthalpy change is the heat of vaporization (_H vap ):

Where Does the Heat Come from?

• Any change in a systemís total energy occurs through changes in  the kinetic and potential energy components:

• A moleculeís E k contributions come from its motion through space,  the rotation and the vibration of the molecule.

• E p contributions are forces in atoms between nuclei and electrons,  between the nucleons and between atoms in each chemical bond.

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