GITAM, Department of Engineering Physics

Heat and Work

            Heat is a form of energy which flows from one body to another on account of temperature difference between them. Thus the flow of heat is a non-mechanical energy transfer.

            But if a system loses energy by other methods, generally, by working against external mechanical forces, it is said to do work. Thus work is the transfer of energy without a temperature difference.


  1. Heat and work are both transient phenomenon. Systems do not possess heat or work.
  2. When a system undergoes a change, heat is transferred or work is done.
  3. Heat and work are boundary phenomenon. They are observed at the boundary of the system.
  4. Heat and work represent the energy crossing the boundary of the system.
  5. Heat and work are path functions and hence they are exact differentials.
  6. It is customary to represent work done by the system as +ve while work done on the system as –ve. Similarly heat flowing into the system as +ve and heat flowing out of the system as –ve.