Thermodynamics Thermodynamics is the study of systems involving energy in the form of heat and work. A good example of a thermodynamic system is gas confined by a piston in a cylinder.
Thermal equilibrium is an important concept in thermodynamics.
When two systems are in thermal equilibrium, there is no net heat transfer between them. This occurs when the systems are at the same temperature. In other words, systems at the same temperature will be in thermal equilibrium with each other. The first law of thermodynamics relates changes in internal energy to heat added to a system and the work done by a system. We've talked about how heat can be transferred, so you probably have a good idea about what Q means in the first law.