Difference Between Equilibrium and Steady State

The key difference between equilibrium and steady state is that in equilibrium, the concentrations of all components are being held constant whereas, in steady state, only some components are kept constant.

When one or more reactants are converted to products, they may go through different modifications and energy changes. The chemical bonds in the reactants are broken, and new bonds are formed to generate products that are totally different from the reactants. This is what we call a chemical reaction. Equilibrium and steady state are important chemical concepts regarding different chemical reactions.

1. Overview and Key Difference
2. What is Equilibrium
3. What is Steady State
4. Side by Side Comparison – Equilibrium vs Steady State in Tabular Form
5. Summary

What is Equilibrium?

Some reactions are reversible, while some reactions are irreversible. In a reaction, reactants are converted to products. In some reactions, the reactants generate again from the products. We name this type of reactions as reversible. In irreversible reactions, once the reactants are converted to products, they do not regenerate again from products.

In a reversible reaction, when reactants are transformed into products, we call it forward reaction. When products are transformed into reactants, we call it a backward reaction. When the rate of forward and backward reactions is equal, then the reaction is at equilibrium. Therefore, the amount of reactants and products do not change over a period of time.

Difference Between Equilibrium and Steady State

Figure 01: Thermal Equilibrium

Reversible reactions always tend to come to equilibrium and maintain that equilibrium. When the system is at equilibrium, the amount of products and the reactants do not have to be necessarily equal. There can be a higher amount of reactants than products or vice versa. The only requirement in an equilibrium equation is maintaining a constant amount from both over time. For a reaction in equilibrium, we can define an equilibrium constant, which is equal to the ratio between the concentration of products and concentration of reactions.

What is Steady State?

Consider a reaction in which reactant A goes to the product C via an intermediate B. In a reaction like this, B is formed by A, and then it undergoes depletion to form C. Before the reaction begins, there is only A, and B slowly starts to build up. However, with time, the amount of A is reduced, and C is increased, but the amount of B remains approximately the same over time. In this state, as soon as more B forms, it will deplete to give C at a rapid rate maintaining a steady state concentration. Thus, rate of synthesis of B = rate of consumption of B.

A ⟶ B ⟶ C

Steady state assumption: d(B)/dt = 0.

What is the Difference Between Equilibrium and Steady State?

Equilibrium and steady state are important chemical concepts. The key difference between equilibrium and steady state is that in equilibrium, the concentrations of all components are held constant whereas, in steady state, only some components are kept constant. In equilibrium, the concentrations of components are constant because the reaction rates are equal in the forward and backward reaction. In steady state, only some components are constant because its synthesis rate and consumption rate are equal. For this, the reactions need not necessarily be in equilibrium.