A single, honest reference for General Chemistry. Formulas are grouped the way a real course teaches them, with the assumptions and units written next to each equation so you never guess when to use which form.
Every formula below is written in the form General Chemistry courses actually use. Read the small note next to each one — the assumptions (STP, dilute solution, constant temperature) are where most mistakes start.
Stoichiometry & the mole
Moles from mass
m in grams, M in g/mol.
n = m / M
Moles of a gas at STP
STP = 0 °C, 1 atm.
n = V / 22.4 L
Particles from moles
Nₐ = 6.022 × 10²³ mol⁻¹.
N = n · Nₐ
Percent yield
% yield = (actual / theoretical) × 100
Molarity
M = n_solute / V_solution (L)
Dilution
Same solute before and after.
M₁V₁ = M₂V₂
Gas laws
Ideal gas law
R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K).
PV = nRT
Combined gas law
T in kelvin.
P₁V₁ / T₁ = P₂V₂ / T₂
Dalton's law
P_total = ΣPᵢ
Mole fraction / partial pressure
Pᵢ = xᵢ · P_total
Graham's law
rate₁ / rate₂ = √(M₂ / M₁)
Thermochemistry
Heat transfer
c is specific heat capacity.
q = m · c · ΔT
Phase change heat
q = n · ΔH_phase
Enthalpy of reaction (Hess)
ΔH_rxn = ΣΔH_f(products) − ΣΔH_f(reactants)
Gibbs free energy
ΔG < 0 → spontaneous.
ΔG = ΔH − TΔS
ΔG from equilibrium
ΔG° = −RT ln K
Equilibrium
Equilibrium constant
K = [products]^a / [reactants]^b
Reaction quotient
Q — same form as K, but at any moment
Kp ↔ Kc
Δn = mol gas products − mol gas reactants.
Kp = Kc (RT)^Δn
Le Chatelier
Stress → shift that partially undoes it
Acids, bases, and buffers
Water autoionization
Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C
pH / pOH
pH = −log[H⁺], pH + pOH = 14
Weak acid
Ka = [H⁺][A⁻] / [HA]
Henderson–Hasselbalch
Buffers only.
pH = pKa + log([A⁻] / [HA])
Kinetics
Rate law
rate = k[A]^m[B]^n
First-order integrated
ln[A] = ln[A]₀ − kt
Second-order integrated
1/[A] = 1/[A]₀ + kt
Half-life (1st order)
t₁/₂ = 0.693 / k
Arrhenius
k = A · e^(−Ea / RT)
Electrochemistry
Cell potential
E°_cell = E°_cathode − E°_anode
ΔG and E°
F = 96 485 C/mol.
ΔG° = −nFE°
Nernst equation
E = E° − (RT / nF) ln Q = E° − (0.0592 / n) log Q at 25 °C
Faraday's law
moles deposited = (I · t) / (n · F)