Classify each change of state(melting, freezing, vaporazation, condensation, sublimation, deposition,ionization, de-ionization) as endothermic or exothermic

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t-nez eNotes educator| Certified Educator

Endothermic processes absorb heat and exothermic processes release heat to the surroundings.

Of the changes of state, melting, vaporization and sublimation are all endothermic because they all require an input of heat energy. 

The reverse of those phase changes, condensation, freezing and deposition, are all exothermic. Heat is released by these reactions. 

(Note the sublimation is the change from solid directly to gas and deposition is the change from gas directly to solid, without a liquid phase.)

Of the other changes, ionization is endothermic because energy is required to remove an electron. I assume that by deionization you mean the gaining of electrons. This is an exothermic process. 

You've probably noticed that the reverse of an endothermic process is exothermic and vice versa. The same is true of chemical reactions.

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