Difference Between Heat And Work


What is heat?

Heat is the form of energy majorly due to temperature differences or increase in molecular kinetic energy. In other words, heat is energy transferred from one system to another solely by reason of a temperature difference between the systems. Heat exists only as it crosses the boundary of a system and the direction of heat transfer is from higher temperature to lower temperature. For thermodynamics sign convention, heat transferred to a system is positive; Heat transferred from a system is negative.

The heat needed to raise a object’s temperature from T1 to T2 is:

Q = cp m (T2 – T1)


cp = specific heat of the object

m = mass of the object

What is work?

In thermodynamics, work performed by a system is the energy transferred by the system to its surroundings. Work is a form of energy, but it is energy in transit. A system contains no work, and work is a process done by or on a system. In general, work is defined for mechanical systems as the action of a force on an object through a distance.

W = F . d


W = work (J)

F = force (N)

d = displacement (m)

Like heat, Work is an energy interaction between a system and its surroundings and associated with a process. In thermodynamics sign convection, work transferred out of a system is positive with respect to that system. Work transferred in is negative.

Also Read: Difference Between Heat and Temperature

Heat vs Work

Description Heat is the transfer of thermal energy between systems. Work is the transfer of mechanical energy between two systems.
Conversion Heat cannot be converted 100% into work. Work cannot be converted 100% into heat.
Form Heat is a low-quality energy. Work is a high-quality energy.
Transfer Temperature difference is the driving force for heat transfer. Displacement or change in position is behind the work transfer.
Nature Heat is associated with the random motion of particles. Work is the energy of ordered motion in one direction.
Requirement Heat requires temperature difference. Work requires force and displacement.
Adiabatic System Being zero for an adiabatic system, cannot affect its temperature. Can cause a temperature rise in an adiabatic system.
Sign In universal sign convention, work done by system is considered positive. In sign convention, heat transferred to a system is considered to be positive.

Similarities Between Heat And Work

  • Both heat and work are forms of energy between system and surrounding.
  • Both the heat and work energies can flow.
  • The unit of measurement for both is Joules.
  • Both are path dependent, it does not depend upon the end state of the system.
  • Both are boundary phenomenon.


Heat is the transfer of thermal energy between systems or objects, while work in physics it’s the transfer of mechanical energy. But the work in thermodynamics is different from the work in physics. The work in thermodynamics is the energy transferred by systems or objects to their surroundings.