The term Free energy includes:
- The thermodynamics term "free energy" denotes the total amount of energy which is used up or released during a chemical reaction. This describes the total energy of a system which is available for "useful work".
- Helmholtz free energy : Work content of any system.
- Gibbs free energy : State function of any system.
- "Free energy" generally means that a primary energy source is "free" (i.e. does not cost anything) for consumption. Free energy is, usually, produced in perpetual motion machines and these energy inquiries usually encourage serious discussion on the topic.
- Free energy, in a strict sense, is energy directly transceived from the environment, and utilized without any artificial aid (sometimes referred to as "radiant energy"). In a technical sense, free energy means an energy source supplied directly by the environment in unlimited quantity (and this can not be depleted). Free energy here is equated with renewable energy, which is energy from a source which is not subject to depletion and does not include energy sources which are dependent upon limited resources.