(1) After baking the mirror, the temperature of the mirror will rise, and the water vapor will not become small drops due to cold, which is convenient for observation. Therefore, the purpose of this is to prevent the liquefaction of water vapor.

② In order to "freeze" the place where the operation is performed, the temperature of the place where the operation is performed should be lowered. Liquid chloroethane can boil at room temperature, and the boiling should absorb heat to reduce the temperature of the place where the operation is carried out.

So the answer is: liquefaction; Boiling absorbs heat.