Definition of steady state

If during the course of a chemical reaction the concentration of an intermediate remains constant, the intermediate is said to be in a steady state. In a static system a reaction intermediate reaches a steady-state if the processes leading to its formation and those removing it are approximately in balance. The steady-state hypothesis leads to a great simplification in reaching an expression for the overall rate of a composite reaction interms of the rate constants for the individual elementary steps. Care must be taken to apply the steady-state hypothesis only to appropriate reaction intermediates. An intermediate such as an atom or a free radical, present at low concentrations, can usually be taken to obey the hypothesis during the main course of the reaction. In a flow system a steady-state may be established even for intermediates present at relatively high concentrations.