m = moles of solute / mass of solvent (kg)
Molality (m) = moles of solute per kilogram of solvent. Unlike molarity (M = mol/L of solution), molality is temperature-independent because it uses mass, not volume. This makes it preferred for colligative property calculations: ΔTb = iKbm, ΔTf = iKfm, π = imRT. Converting between molarity and molality: m = M/(ρ − M×Msolute/1000), where ρ is solution density in g/L. For dilute aqueous solutions at room temperature, m ≈ M because density ≈ 1 kg/L and solute mass is negligible. Molality is also used in thermodynamic equations for activity coefficients and partial molar properties.