Glossary
First Law of Thermodynamics
The first law of thermodynamics introduces the concepts of work, heat, and energy and states that, in a system of constant mass, energy can neither be created nor destroyed, although it may be converted from one form to another. This law is also referred to as the law of conservation of energy.
If a system receives an amount of heat Q, and the work W is done on the system, then the internal energy of the system must have increased by Q + W, independently of what happened to the energy inside the system:
ΔU = Q + W
Or, in differential form, the first law of thermodynamics can be expressed as follows:
dU = dQ + dW