Two other common heat variables are the heat of fusion and the heat of vaporization. Heat of fusion is the heat required to melt a substance at is normal melting temperature, while the heat of vaporization is the heat required to evaporate the substance at its normal boiling point. Chemical work is primarily related to that of expansion. The value of distance times area is actually the volume. If we imagine a reaction taking place in a container of some volume, we measure work by pressure times the change in volume.
Energy can only change form.
Chemically, that usually means energy is converted to work, energy in the form of heat moves from one place to another, or energy is stored up in the constituent chemicals. You have seen how to calculate work. Heat is defined as that energy that is transferred as a result of a temperature difference between a system and its surroundings. If q is positive, we say that the reaction is endothermic, that is, heat flows into the reaction from the outside su rroundings. If q is negative, then the reaction is exothermic, that is, heat is given off to the external surroundings.