Chemistry Formulas
10 essential chemistry formulas with detailed explanations, examples, and when to use them.
Ideal Gas Law
PV = nRT
The ideal gas law relates pressure, volume, amount, and temperature of an ideal gas. It combines Boyle's, Charles's, and Avogadro's laws into one equation and is fundamental for gas calculations.
Mole Calculations
n = m / M
The fundamental relationship between mass, moles, and molar mass. This equation is the gateway to all stoichiometry calculations, converting between measurable mass and moles.
Molarity
M = n / V = mol / L
Molarity is the most common concentration unit in chemistry. It expresses concentration as moles of solute per liter of solution and is essential for solution stoichiometry.
Gibbs Free Energy
deltaG = deltaH - T(deltaS)
Gibbs free energy determines reaction spontaneity by combining enthalpy and entropy. A negative deltaG indicates a spontaneous reaction; positive deltaG indicates non-spontaneous.
Rate Law
Rate = k[A]^m[B]^n
The rate law expresses reaction rate as a function of reactant concentrations. The orders (m, n) must be determined experimentally and are not necessarily equal to stoichiometric coefficients.
Arrhenius Equation
k = Ae^(-Ea/RT)
The Arrhenius equation shows how rate constant k depends on temperature and activation energy. It explains why reactions speed up with temperature.
Equilibrium Constant
K = [products]^coefficients / [reactants]^coefficients
The equilibrium constant K expresses the ratio of product to reactant concentrations at equilibrium. Large K means products favored; small K means reactants favored.
Henderson-Hasselbalch Equation
pH = pKa + log([A-]/[HA])
The Henderson-Hasselbalch equation calculates buffer pH from the ratio of conjugate base to weak acid. It's essential for buffer preparation and understanding biological pH control.
Nernst Equation
E = E° - (RT/nF)ln(Q) or E = E° - (0.0592/n)log(Q) at 25°C
The Nernst equation calculates cell potential under non-standard conditions by accounting for concentration effects. It shows how cell voltage changes with reaction quotient Q.
Calorimetry
q = mc(deltaT)
The calorimetry equation calculates heat absorbed or released using mass, specific heat capacity, and temperature change. It's fundamental for determining enthalpy changes experimentally.
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