MATSEC AM Chemistry cheat sheet

MATSEC AM Chemistry - Core Reference

• Mole relations: n = m/M; n = cV (V in dm³); gas at s.t.p.: n = V/22.7 dm³ mol⁻¹; ideal gas: pV = nRT with R = 8.314 J K⁻¹ mol⁻¹.

• Empirical formula from percentage composition: divide each % by atomic mass, divide by the smallest quotient, multiply to reach whole numbers; molecular formula = (empirical formula)ₙ where n = Mᵣ/empirical mass.

• Limiting reagent: convert all reactant amounts to moles, divide by stoichiometric coefficients, the smallest ratio limits; theoretical yield then % yield = (actual/theoretical) × 100.

• Concentration conversions: c₁V₁/n₁ = c₂V₂/n₂ for titrations; ppm = mg solute per kg solution; molality = mol solute per kg solvent (temperature-independent, unlike molarity).

• Acid–base: pH = −log₁₀[H⁺]; pOH = 14 − pH at 298 K; K_w = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴; weak acid [H⁺] = √(K_a·c); buffer pH = pK_a + log([salt]/[acid]).

• Thermochemistry: q = mcΔT; ΔH = −q/n for exothermic sign convention; Hess's law adds enthalpy steps; ΔG = ΔH − TΔS, spontaneous when ΔG < 0.

• Electrochemistry: cell e.m.f. = E°(cathode) − E°(anode); ΔG° = −nFE° with F = 96 500 C mol⁻¹; oxidation occurs at the anode in every cell type.

• Kinetics: rate = k[A]ᵐ[B]ⁿ with orders found by experiment, not stoichiometry; first-order half-life t½ = ln2/k = 0.693/k, independent of initial concentration.

• Equilibrium: K_c and K_p expressions exclude pure solids and liquids; K_p = K_c(RT)^Δn(gas); a catalyst changes rate and time-to-equilibrium but not the value of K.