Formula Library
Verified chemistry formulas — each page shows equation, purpose, variables, units, conditions, rearrangements, dimensional check, example, common errors, and related resources. Only published, reviewed formulas appear.
Arrhenius Equation
Temperature dependence of rate constant.
chemical-kinetics\bar{M}=\sum f_i M_iAverage Atomic Mass
Weighted average isotopic masses by fractional abundance.
atomic-structureN = n N_AAvogadro Relation
Relate number of entities to amount via Avogadro constant.
mole-stoichiometryP_1 V_1 = P_2 V_2Boyle's Law
Pressure-volume inverse at constant n,T.
gases-gas-lawsq = m c \Delta TCalorimetry Heat
Heat from mass, specific heat, temperature change.
thermochemistry-thermodynamics\frac{V_1}{T_1}=\frac{V_2}{T_2}Charles's Law
Volume-temperature direct at constant P.
gases-gas-laws\frac{P_1 V_1}{T_1}=\frac{P_2 V_2}{T_2}Combined Gas Law
Combine Boyle, Charles, Gay-Lussac for constant n.
gases-gas-lawsP_{tot}=\sum P_i,\ P_i = x_i P_{tot}Dalton's Partial Pressures
Total pressure = sum of partials; partial from mole fraction.
gases-gas-lawsN = N_0 e^{-kt}, \ln\frac{N_0}{N}=ktRadioactive Decay Law
Amount remaining after time t via exponential decay.
nuclear-chemistry\rho = \frac{m}{V}Density
Relate mass and volume to characterize substances.
matter-measurementc_1 V_1 = c_2 V_2Dilution Equation
Relate concentrations before and after dilution (moles conserved).
solutions-concentration\text{ratio}=\frac{\% /M}{smallest}Empirical Formula Relation
Determine simplest whole-number ratio from percent composition.
mole-stoichiometryK_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}Equilibrium Constant Kc
Ratio of product/reactant concentrations at equilibrium.
chemical-equilibriumm = \frac{Q M}{n F} = \frac{I t M}{n F}Faraday's Electrolysis
Mass deposited/evolved in electrolysis.
redox-electrochemistry\Delta G = \Delta H - T\Delta SGibbs Energy
Predict spontaneity and maximum non-PV work.
thermochemistry-thermodynamicst_{1/2}=\frac{\ln 2}{k}Half-Life (First-Order)
Time for half of nuclei/amount to decay for first-order.
nuclear-chemistrypH = pK_a + \log\frac{[A^-]}{[HA]}Henderson–Hasselbalch
pH of buffer from conjugate pair ratio; approximations limited.
acids-bases-buffers\Delta H_{rxn}=\sum \Delta H_{steps}Hess's Law
Sum stepwise enthalpies to find overall reaction enthalpy.
thermochemistry-thermodynamicsPV = nRTIdeal Gas Law
Relate pressure, volume, amount, temperature for an ideal gas.
gases-gas-lawsK_{sp}=[A^+]^a[B^-]^bKsp Expression
Solubility product for sparingly soluble salt.
solubility-precipitationb = \frac{n}{m_{solvent}}Molality
Concentration per mass solvent, temperature independent.
solutions-concentrationc = \frac{n}{V}Molarity
Concentration as amount per volume of solution.
solutions-concentrationn = \frac{m}{M}Moles from Mass
Convert measurable mass to amount of substance.
mole-stoichiometryE = E^\circ - \frac{RT}{nF}\ln QNernst Equation
Cell potential under nonstandard conditions.
redox-electrochemistry\%E = \frac{m_E}{m_{tot}} \times 100Percent Composition
Mass fraction of an element in a compound.
mole-stoichiometry\%_{yield}=\frac{m_{actual}}{m_{theoretical}}\times100Percent Yield
Compare actual to theoretical product mass.
mole-stoichiometryE = h\nu = \frac{hc}{\lambda}Photon Energy
Energy of photon from frequency or wavelength.
atomic-structure\text{rate}=k[A]^m[B]^nRate Law
Express rate dependence on concentrations with orders.
chemical-kineticsQ = \frac{[C]^c[D]^d}{[A]^a[B]^b}_{non-eq}Reaction Quotient Q
Compare current state to equilibrium; predict direction.
chemical-equilibriumAll formulas include purpose, conditions, rearrangements, dimensional check, worked example, and common errors. Linked calculators appear only when real.