M.5—Key quantities, symbols and units

Use the standard symbol and SI unit for each quantity: mass m (g or kg), volume V (dm³ or m³), amount n (mol), temperature T (K), pressure p (Pa), charge Q (C), potential difference E (V) and time t (s).

Constants and chemical quantities such as Nₐ, F, R, Kᵥ, Ar, Mr, E° and ΔH have fixed meanings; write units beside intermediate values so a mismatch is visible.

In Q = It, current is in amperes and time in seconds; in n = cV, convert V to dm³ when c is mol dm⁻³.

A symbol is not interchangeable with a similarly named quantity: E° is an electrode potential, while ΔH is an enthalpy change.