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. You might also remember the terms kinetic energy and potential energy .
Potential energy is stationary, stored energy.
If you think of a ball sitting on the edge of a table, it has potential energy in the energy possible if it falls off the table. Potential energy can be transformed into kinetic energy if and when the ball actually rolls off the table and is in motion. The total energy of the system is defined as the sum of kinetic and potential energies. A state property is a quantity whose value is independent of the past history of the substance. Typical state properties are altitude, pressure, volume, temperature, and internal energy.