# Equilibrium --- **Equilibrium** describes a state of balance between opposing forces. It is does not describe a state where two forces have *ceased moving*, but where the two opposing motions happen at the same rate, such that there is not measurable difference *over time*. The [[thermodynamics#The Second Law|second law of thermodynamics]] states that the approach to equilibrium is an inexorable process that can be defined as a system moves towards a state of maximum entropy. Once this state is achieved, the system is in equilibrium. This tendency toward equilibrium is so fundamental to [[physics]] that the second law is probably the most universal regulator of natural activity known to science. ![[equilibrium.png]] ## Equilibrium in Chemistry In [[chemistry]], particles in [[solution|solution]] will always move with a [[concentration gradient]] in order to achieve equilibrium. ### Chemical Reactions Most [[chemical reaction|chemical reactions]] are reversible. They can proceed in both directions, releasing energy into their environment in one direction, and absorbing it from the environment in the other direction. Reactions achieve equilibrium when the amount of reactants and products become stable, even if there is still reactions and backward reactions happening. ## Equilibrium in Biology Equilibrium can be thought of in biology as [[homeostasis]]. Solutions in [[biology]] will [[membrane transport|diffuse]] across permeable or semipermeable [[plasma membrane|membranes]] in order to achieve equilibrium. [[Osmosis]] describes how water will diffuse across a membrane in order to achieve equilibrium with concentration gradient. ___