← Equilibrium principles in aqueous systems
1 Reading the notation
This standard uses many subscripted K values and log-scale quantities. Here is what each actually means.📖 Symbols used in aqueous equilibria
8 termsCover the right column and check you can say what each one means.
- ⇌ (double half-arrow)
- A reversible reaction at equilibrium, both directions occur at once. Different from →, which means the reaction goes essentially to completion.
- K (equilibrium constant)
- The ratio of products to reactants at equilibrium, each raised to its coefficient. Large K means products are favoured. K changes ONLY with temperature. Concentration and pressure shift the position of equilibrium, not K.
- Ka / Kb
- Acid and base dissociation constants: how far a weak acid or base ionises. Larger Ka = stronger acid. For a conjugate pair, Ka × Kb = Kw.
- Kw
- The ionic product of water: [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C.
- Ks (solubility product)
- The equilibrium constant for a sparingly soluble solid dissolving. A precipitate forms when the ionic product exceeds Ks.
- p (the p in pH, pKa, pOH)
- An operator meaning −log₁₀. pH = −log[H⁺]; pKa = −log Ka. The minus sign INVERTS the scale: a smaller pKa means a larger Ka, i.e. a stronger acid.
- [X] (square brackets)
- The concentration of X in mol L⁻¹. [H⁺] is the hydrogen-ion concentration. Here square brackets always mean concentration, not mathematical grouping.
- mol L⁻¹
- Moles per litre. The ⁻¹ means “per”, so L⁻¹ is “per litre”.