Master essential chemistry formulas with clear explanations, variable definitions, and practical examples. Each formula links to interactive calculators for hands-on practice.
M = n / V
Calculate molar concentration of solutions
m = n / kgsolvent
Calculate molal concentration
N = equivalents / L
Equivalents-based concentration
M1V1 = M2V2
Calculate dilution concentrations
% = (msolute / msolution) × 100
Calculate mass percentage
χ = ni / ntotal
Calculate mole fraction in mixtures
ρ = m / V
Relate mass and volume of substances
ppm = (msolute/msolution) × 106
Parts per million concentration
ppb = (msolute/msolution) × 109
Parts per billion concentration
Ksp = Π[ion]coeff
Equilibrium solubility of salts
% Yield = (Actual / Theoretical) × 100
Calculate reaction efficiency
Simplest whole number ratio
Determine simplest formula
Compare mole ratios
Find limiting reagent
MW = sum atomic masses
Calculate molar mass
Molecular = Empirical × factor
Get formula from empirical + MW
% element = (mass element / mass compound) × 100
Elemental makeup by mass
Max product from stoichiometry
Calculate maximum product
DU = (2C + 2 + N - H - X) / 2
Count rings + double bonds
Find formula from CO₂ and H₂O
Empirical formula determination
% Error = |Exp - Theo| / Theo × 100
Measure experimental accuracy
PV = nRT
Relate pressure, volume, and temperature
P1V1/T1 = P2V2/T2
Gas behavior under changing conditions
Ptotal = P1 + P2 + ...
Calculate partial pressures
r1/r2 = √(M2/M1)
Gas effusion and diffusion rates
P ∝ 1/V (constant T)
Pressure-volume relationship
V ∝ T (constant P)
Volume-temperature relationship
P ∝ T (constant V)
Pressure-temperature relationship
(P + a(n/V)^2)(V - nb) = nRT
Real gas corrections
ρ = (P M) / (R T)
Density via ideal gas relation
vrms = √(3RT/M)
Molecular speed in gases
Vm = 22.4 L/mol at STP
Volume of one mole of gas
V / n = constant
Volume-mole relationship
ΔG = ΔH - TΔS
Predict reaction spontaneity
q = mcΔT
Calculate heat absorbed or released
ln(K2/K1) = -(ΔH/R)(1/T2 - 1/T1)
Temperature dependence of K
ln(P2/P1) = (ΔH/R)(1/T1 - 1/T2)
Vapor pressure vs temperature
ΔH = Σ(products) - Σ(reactants)
Reaction heat from DeltaHf
ΔS = Σ(products) - Σ(reactants)
Disorder change from S° data
ΔH = Σ(broken) - Σ(formed)
Estimate ΔH from bond energies
ΔHtotal = ΔH₁ + ΔH₂ + ...
Sum intermediate steps
Born-Haber cycle
Ionic solid stability
q = m c ΔT
Heat transfer in chemical processes
k = Ae-Ea/RT
Temperature effect on rate constants
Rate = k[A]m[B]n
Reaction rate dependence
t1/2 = 0.693/k (1st order)
Calculate reaction half-life
N = N₀ e−λt; λ = ln2/t1/2
Remaining quantity vs time
0th, 1st, 2nd order kinetics
Concentration vs time
v = (Vmax[S]) / (Km + [S])
Enzyme kinetics
K = [products] / [reactants]
Chemical equilibrium
Compare Q to K
Predict reaction direction
Rate = Z × f × p
Molecular basis of reaction rates
Slowest step controls rate
Reaction mechanism bottleneck
Equilibrium shift from stress
Response to concentration, P, T
Solubility suppression
Shared ion reduces solubility
A = εℓC
Absorbance, path length, concentration
λ = h / p
Matter wave wavelength
Δx Δp ≥ ℏ / 2
Position-momentum limit
FC = V - N - B/2
Charge distribution in molecules
Aufbau, Pauli, Hund's rule
Orbital filling principles
sp, sp², sp³ orbitals
Determine hybrid orbital types
En = -13.6 Z² / n²
Energy levels in hydrogen-like atoms
d-orbital splitting, Δ
Coordination complex stability
Electron pair repulsion
Predict molecular geometry
I = 1/2 Σ ci zi²
Total ion concentration measure
Electron pair repulsion
Predict molecular geometry
μ = q × d
Molecular polarity
Kp = [organic] / [aqueous]
Distribution between solvents
a = γ × [C]
Non-ideal solution correction
E = Δm c²
Nuclear stability from mass defect
1/λ = RH(1/n₁² - 1/n₂²)
Hydrogen spectral lines
E = h ν
Photon energy and frequency
nλ = 2d sinθ
X-ray diffraction
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