Definition

1. Noun:
   • A principle in physical chemistry: The law of chemical equilibrium states that for a reversible chemical reaction at equilibrium and constant temperature, the ratio of the product of the concentrations (or partial pressures) of the products to the product of the concentrations (or partial pressures) of the reactants, each raised to the power of its stoichiometric coefficient, is a constant. This constant is known as the equilibrium constant (K).

Usage Examples

• Noun:
  • The law of chemical equilibrium allows chemists to predict the concentrations of reactants and products in a closed system.
  • According to the law of chemical equilibrium, if you increase the concentration of a reactant, the system will shift to produce more products to re-establish equilibrium.
  • Understanding the law of chemical equilibrium is fundamental for designing industrial chemical processes like the Haber process for ammonia synthesis.

Advanced Usage

• Mathematical Expression: The law is quantitatively expressed as the equilibrium constant expression. For a general reversible reaction ( aA + bB \rightleftharpoons cC + dD ), the law states: ( Kp = \frac{(PD)^d}{(PB)^b} ) for partial pressures.
• "To obey the law of chemical equilibrium": A system is said to obey this law when the calculated ratio from experimental concentrations matches the known equilibrium constant for the reaction at that temperature.
  • The reaction mixture was analyzed and found to obey the law of chemical equilibrium, confirming the system had reached a steady state.

Variants and Related Words

• Equilibrium Constant (K) (n): The numerical value of the constant ratio defined by the law of chemical equilibrium.
• Reaction Quotient (Q) (n): A ratio calculated using the same formula as K but with initial or non-equilibrium concentrations. Comparing Q to K predicts the direction a reaction will shift.
• Le Chatelier's Principle (n): A related principle that predicts how a system at equilibrium responds to changes in concentration, pressure, or temperature.

Synonyms

• Equilibrium Law: A direct synonym.
• Mass Action Law: A historical and closely related term, though sometimes considered broader as it also relates to reaction rates.

Related Phrases

• To apply the law of chemical equilibrium: To use the principle to solve a problem.
  • We can apply the law of chemical equilibrium to calculate how much product will form.
• To be governed by the law of chemical equilibrium: Describes a reversible reaction system.
  • The final proportions of gases in the container are governed by the law of chemical equilibrium.

Noun

1. (chemistry) the principle that (at chemical equilibrium) in a reversible reaction the ratio of the rate of the forward reaction to the rate of the reverse reaction is a constant for that reaction