Gas Stoichiometry Calculator
Gas stoichiometry uses the molar volume of an ideal gas at STP (22.414 L per mole at 0 degrees C and 1 atm) together with balanced equation mole ratios to convert between volumes and amounts of gaseous reactants and products. Enter the volume of reactant gas at STP, the mole coefficient of the reactant in the balanced equation, and the mole coefficient of the product to find the volume of product gas produced at STP.
Gas stoichiometry formula
moles reactant = V(reactant) / 22.414 L/mol moles product = moles reactant * (coeff product / coeff reactant) V(product) = moles product * 22.414 L/mol
At STP (0 C, 1 atm), the molar volume of an ideal gas is 22.414 L/mol. Mole ratios come from the balanced chemical equation coefficients.
Worked example: hydrogen combustion
- Reaction: 2 H(2)(g) + O(2)(g) produces 2 H(2)O(g).
- If 44.828 L of H(2) is burned at STP: moles H(2) = 44.828 / 22.414 = 2.00 mol.
- Mole ratio H(2)O : H(2) = 2:2 = 1:1, so moles H(2)O = 2.00 mol.
- Volume H(2)O(g) at STP = 2.00 * 22.414 = 44.83 L.
Frequently asked questions
What is gas stoichiometry?
Gas stoichiometry applies the mole ratios from a balanced chemical equation to calculate volumes of gaseous reactants or products. At STP, 1 mol of any ideal gas occupies 22.414 L, allowing direct volume-to-mole conversions.
How do I use mole ratios from a balanced equation?
The coefficients in a balanced equation give the mole ratio of reactants to products. For example, in 2H2 + O2 - 2H2O, the ratio of H2 to O2 is 2:1, and the ratio of O2 to H2O is 1:2.
Can I compare volumes directly without converting to moles?
Yes, if all species are gases at the same temperature and pressure, volumes are proportional to mole ratios (Avogadro's law). 2 L of H2 reacts with 1 L of O2 to produce 2 L of H2O vapor.
Does the molar volume change with conditions?
Yes. At STP (0 C, 1 atm), the molar volume is 22.414 L/mol. At SATP (25 C, 100 kPa), it is 24.465 L/mol. For conditions other than STP, use the ideal gas law PV = nRT.
What is the limiting reactant in gas stoichiometry?
The limiting reactant is the reactant that is completely consumed first and determines the maximum amount of product formed. Identify it by converting all reactant amounts to moles of product and taking the minimum.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.