Definition of Heat
Heat is defined as the energy transferred from one system to another by thermal interaction. It is measured in joules (J). Heat is transferred by conduction or radiation . This means that when a high temperature body is brought into contact with a low temperature body, heat flows from the high temperature body to the low temperature body spontaneously until their temperatures are equivalent. The high temperature body loses thermal energy/triangle E and the low temperature body acquires the same amount of energy. The system is then said to be at thermal equilibrium . Therefore, it can be said that heat is a process that involves the transference of thermal energy from a high temperature thermal body to a low temperature thermal body. The transfer of heat can be described by saying that triangle E joules of heat have passed from the high temperature body to the low temperature body.
Definition of Work
Work is the transfer of energy by any process other than heat. Like heat, the unit measurement for work is joules. There are many forms of work among them including mechanical, electrical, and gravitational work. For our purposes, we are concerned with thermal work which is the work done in an enclosed chemical system. In this type of system, work is defined as the change in the volume (V) within the system (in liters) multiplied by a pressure (P) variable:
Heat and work are related. Work can be completely converted into heat, but heat can only be partially converted into work.
Scientists and engineers have been able to exploit the principles of thermochemistry to development technologies ranging from hot/cold packs to gasoline powered combustion engines.
Work can be defined in many terms, but in chemistry is most applicable when pressure and volume with gases. The product of volume (V) and pressure (P) is an energy. When volume changes (from a to b) at constant pressure, the energy change that results is a value of work:
Relationship Between Heat and Work
For a closed system, its change in internal energy (∆U) is related to heat (Q) and work (W) as:
This means that the total energy within a system is affected by the sum of two possible transfers: heat and work.