Chemical Equilibrium
Definition and meaning of Chemical Equilibrium in chemistry.
Chemical equilibrium is the state of a reversible reaction in which the forward and reverse reactions occur at equal rates, so the concentrations of reactants and products no longer change over time.
In more detail
Equilibrium is dynamic, not static: both the forward and reverse reactions keep happening at the molecular level, but because their rates are equal there is no net change in composition. The position of equilibrium is quantified by the equilibrium constant, K, which relates the concentrations (or partial pressures) of products and reactants at a given temperature. Le Chatelier's principle describes how a system at equilibrium responds to a change in concentration, pressure, volume, or temperature by shifting to partially counteract the disturbance.
Key facts
| Field | Physical Chemistry |
|---|---|
| Governing constant | K (equilibrium constant), e.g. Kc or Kp |
| Key principle | Le Chatelier's principle |
| Nature | Dynamic, not static, reactions continue in both directions |
In the Haber process, N2(g) + 3H2(g) ⇌ 2NH3(g), equilibrium is reached when ammonia forms at the same rate it decomposes back into nitrogen and hydrogen; the equilibrium constant Kc expresses the fixed ratio of product to reactant concentrations at that temperature.
Frequently asked questions
Does chemical equilibrium mean the reaction has stopped?
No. Equilibrium is dynamic: the forward and reverse reactions continue at equal rates, so overall concentrations stay constant even though individual molecules keep reacting.
What does the size of K indicate?
A large K (K >> 1) means products are favored at equilibrium, while a small K (K << 1) means reactants are favored; K is constant at a given temperature but changes if temperature changes.