Heat and work are two different ways of transferring energy from one system to another. The the distinction between Heat and Work is important in the field of thermodynamics. Heat is the transfer of thermal energy between systems, while work is the transfer of mechanical energy between two systems. This distinction between the microscopic motion (heat) and macroscopic motion (work) is crucial to how thermodynamic processes work. Heat can be transformed into work and vice verse (see mechanical equivalent of heat), but they aren't the same thing. The first law of thermodynamics states that heat and work both contribute to the total internal energy of a system, but the second law of thermodynamics limits the amount of heat that can be turned into work.
Heat and work each have their own distinct properties, and they differ in how they affect a system. These are listed and compared below:[1]
Work (W) | Heat (Q) | |
---|---|---|
Interaction | Mechanical | Thermal |
Requires | Force and Displacement | Temperature difference |
Process | Macroscopic pushes and pulls | Microscopic collisions |
Positive value | W > 0 when a gas is compressed. Energy is transferred into system. | Q > 0 when the environment is at a higher temperature than the system. Energy is transferred into system. |
Negative value | W < 0 when a gas expands. Energy is transferred out of system. | Q < 0 when the system is at a higher temperature than the environment. Energy is transferred out of system. |
Equilibrium | A system is in mechanical equilibrium when there is no net force or torque on it. | A system is in thermal equilibrium when it is at the same temperature as the environment. |
Bethel Afework, Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: July 21, 2018
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