Free energy, in the context of physics and thermodynamics, refers to the energy available in a system to do useful work. It is also known as Gibbs free energy or simply G. Free energy takes into account both the enthalpy (total heat content of a system) and the entropy (degree of disorder) of the system, providing a measure of the spontaneity of a process or reaction under constant temperature and pressure conditions. A negative change in free energy (ΔG < 0) indicates that a reaction is spontaneous and can occur without external energy input, while a positive ΔG indicates a non-spontaneous reaction that requires energy input to proceed.
The term “free energy” can sometimes be misunderstood outside of its scientific context. In scientific discourse, free energy specifically refers to the thermodynamic potential that can be used to perform work, particularly in physical and chemical processes. It does not imply energy that is cost-free or available without any effort or expenditure.
No energy is truly free in the sense of being costless or universally available without limits. In physics and engineering, free energy refers to the thermodynamic concept described above, which quantifies the energy available to do work in a system. All forms of energy involve resources, whether natural resources, human labor, or technological inputs, and typically incur costs or have environmental impacts associated with their extraction, conversion, and utilization.
In biochemistry notes, free energy often refers to Gibbs free energy (ΔG), which plays a crucial role in biochemical reactions. ΔG helps determine whether biochemical reactions, such as enzyme-catalyzed processes or metabolic pathways, are energetically favorable (spontaneous) or require additional energy input to proceed. Biochemical reactions that release energy (ΔG < 0) can drive cellular processes such as ATP synthesis, while reactions with positive ΔG require energy input to occur.
The unit of free energy, ΔG, is typically expressed in joules (J) in the International System of Units (SI). In biochemical contexts, particularly in relation to enzymatic reactions and metabolic pathways, free energy changes (ΔG) are commonly reported in kilojoules per mole (kJ/mol) to reflect the energy change per mole of reactants or products involved in the reaction. The unit joule represents the amount of energy transferred or expended when applying a force of one newton over a distance of one meter, providing a standardized measure of free energy changes in scientific calculations and analyses.