Processes occur when systems change from one [[State|state]] to another. States define the physical characteristics of a system at a specific time. System changes are due to [[Energy|energy]] transfer between the system and its surroundings. A quasi-equilibrium process assumes that for any instant during the process the system is at thermodynamic equilibrium. Some common quasi-equilibrium processes are: - **Isothermal:** Process occurs with a constant temperature - **Isobaric:** Process occurs with a constant pressure - **Isometric:** Process occurs with a constant volume - **Adiabatic:** Process occurs without heat transfer - **Zero work:** Process occurs without any work