In chemistry, the steady state approximation is an estimation of the value of a chemical equilibrium whereby one variable of the chemical reaction is fixed, or placed as a perceived constant, in order to obtain a mathematical value for the end state of many overlapping chemical reactions. This concept is also referred to as the stationary-state approximation in some academic and scientific texts.
Steady state approximation is only intended to operate as a casual differentiator between two analyzed reactions. The calculation is commonly applied in Michaelis-Menten kinetics, which explains the rates at which different enzymes react with one another. It is important to note that the steady state approximation assigns only the intermediate concentration variation at a value almost equal to zero, rather than at an absolute constant. The Faculty of Science at the University of Waterloo states that this set-zero value may still oscillate and produce measured variations, but the values are so small that the calculative variations are negligible in comparison to the fluctuations in the variations of the accompanying reactions. It is only valid to apply the steady state approximation when one measured reaction yields a much faster reaction in comparison to a second analytical solution. The slower reaction is the value that is then almost equal to zero in the equation.