Chemistry equations

Relative atomic mass (Ar)

Average mass of one atom of an element ÷ (1/12 × mass of one atom of 12C)

Relative molecular mass (Mr)

Sum of Ar of all atoms in a molecule

Moles (n)

Number of moles = mass ÷ molar mass (n = m / M)

Moles (conc formula)

n = c × V (mol = concentration × volume)

Ideal gas equation

pV = nRT (p in Pa, V in m³, T in K)

Percentage yield

(actual yield ÷ theoretical yield) × 100

Atom economy

(mass of desired products ÷ total mass of reactants) × 100

Empirical formula

Simplest whole number ratio of atoms of each element

Energy transferred (q)

q = mcΔT (q in J, m in g, c in J/g°C, ΔT in °C)

Enthalpy change per mole

ΔH = -q / n

Equilibrium constant Kc

[a]^A [b]^B ÷ [c]^C [d]^D (products over reactants, concentrations)

pH of a solution

pH = -log[H+]

[H+] from pH

[H+] = 10^-pH

Kw expression

Kw = [H+][OH−]

pH of strong base

pOH = -log[OH−]; then pH = 14 - pOH

Ka expression

Ka = [H+][A−] ÷ [HA]

pKa

pKa = -log(Ka)

Ka from pKa

Ka = 10^(-pKa)

Buffer [H+] formula

[H+] = Ka × [HA] ÷ [A−]

Rate of reaction

Rate = change in concentration ÷ time

Rate constant from rate law

rate = k[A]^m[B]^n

Arrhenius equation

k = Ae^(-Ea/RT)

Half-life

t1/2 = ln(2)/k for first order reactions

Standard electrode potential

E°cell = E°(reduced) - E°(oxidised)

Gibbs free energy

ΔG = ΔH - TΔS (ΔG in J or kJ, T in K)

Entropy change

ΔS = ΣS(products) - ΣS(reactants)

Lattice enthalpy (Born-Haber)

E.g., ΔHf = ΔHat + IE + EA + ΔHlatt

Equilibrium constant Kp

Kp = (p products)^coeff ÷ (p reactants)^coeff