PlanetPhysics/First Law of Thermodynamics
The amount of work required to change the state of an otherwise adiabatically isolated system depends only on the initial and final states, and not on the means by which the work is performed, or on the intermediate stages through which the system passes.
Transformations between different equilibrium states can be achieved by applying work or heat to the system. The first law states that both work and heat are forms of energy, and that the total energy is conserved.
References
This is a derivative work from [1] a Creative Commons Attribution-Noncommercial-Share Alike 3.0 work
[1] MIT OpenCourseWare, 8.333 Statistical Mechanics I: statistical mechanics of particles, Fall 2007