Glossary
Equilibrium
A dynamic state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, leading to constant concentrations of reactants and products.
Example:
When a bottle of soda is opened, CO₂ escapes, but if sealed, the dissolved CO₂ and gaseous CO₂ reach equilibrium where the rate of CO₂ dissolving equals the rate of CO₂ escaping.
Equilibrium Constant (K)
A value that expresses the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their stoichiometric coefficients.
Example:
For the reaction A ⇌ B, if at equilibrium [B] is much higher than [A], the equilibrium constant (K) would be a large number, indicating a product-favored reaction.
K < 1
Indicates that at equilibrium, the concentration of reactants is greater than the concentration of products, meaning the reaction is reactant-favored.
Example:
If the K for a reaction is 1.0 x 10⁻⁵, it means the reaction barely proceeds to products, and the system is largely reactant-favored.
K = 1
Indicates that at equilibrium, the concentrations of products and reactants are roughly equal.
Example:
While rare, if a reaction has a K = 1, it suggests that at equilibrium, you'd find comparable amounts of both starting materials and final substances.
K > 1
Indicates that at equilibrium, the concentration of products is greater than the concentration of reactants, meaning the reaction is product-favored.
Example:
A reaction with a K value of 1.0 x 10³ will have a high yield of products at equilibrium, demonstrating it is strongly product-favored.
Product-Favored
A reaction at equilibrium where the concentration of products is significantly greater than the concentration of reactants.
Example:
If you mix a strong acid and a strong base, the neutralization reaction is highly product-favored, meaning almost all reactants convert to salt and water.
Reactant-Favored
A reaction at equilibrium where the concentration of reactants is significantly greater than the concentration of products.
Example:
The dissociation of a weak acid like acetic acid in water is reactant-favored, meaning only a small fraction of the acid molecules break apart into ions.
Reversible Reactions
Chemical reactions where reactants form products, and simultaneously, products can convert back into reactants.
Example:
The formation of ammonia from nitrogen and hydrogen (N₂ + 3H₂ ⇌ 2NH₃) is a classic example of a reversible reaction where both the forward and reverse processes occur.