Common Chemistry Formulas for Students
By the Periodixy Editorial Team · Last reviewed July 10, 2026
This is the formula sheet we wish every chemistry student had on day one: the equations that solve 90% of homework problems, each with its units and a quick note on when to use it.
Moles and mass
Moles from mass
n = m ÷ M (mol = g ÷ g/mol)
Number of particles
N = n × 6.022 × 10²³
The mole is the bridge between the lab scale (grams) and the atomic scale (particles). Molar mass M comes from the periodic table — or the Molar Mass Calculator.
Solutions
Molarity
M = n ÷ V (mol/L)
Dilution
C₁V₁ = C₂V₂
pH
pH = −log[H⁺] • pH + pOH = 14 (at 25 °C)
Gases
Ideal gas law
PV = nRT (R = 0.0821 L·atm/mol·K)
Combined gas law
P₁V₁/T₁ = P₂V₂/T₂ (T in kelvin!)
Molar volume at STP
1 mol of gas ≈ 22.4 L at 0 °C and 1 atm
Reactions and yield
Percent yield
% yield = (actual ÷ theoretical) × 100
Percent composition
% element = (mass of element in formula ÷ molar mass) × 100
Density
d = m ÷ V (g/cm³ for solids/liquids, g/L for gases)
Energy
Heat
q = m × c × ΔT
q = heat (J), m = mass (g), c = specific heat capacity (J/g·°C; water ≈ 4.18), ΔT = temperature change. Positive q means heat absorbed.
Quick energy example
How much heat warms 100 g of water from 20 °C to 80 °C?
- q = 100 g × 4.18 J/g·°C × 60 °C
Answer: ≈ 25,000 J = 25 kJ
Summary
- n = m/M converts mass to moles — the start of nearly every calculation.
- M = n/V and C₁V₁ = C₂V₂ handle solutions.
- PV = nRT rules gases (kelvin only!).
- q = mcΔT covers heating and cooling.