How to Calculate Stoichiometry

Stoichiometry is the quantitative study of the relationships among reactants and products in a chemical reaction. The calculation allows you to determine the amount of a substance that is consumed or produced in a reaction, given the amount of another substance.

The process involves three main steps:

1. Convert Mass to Moles:

   Using the molar mass of the given substance, convert its mass into moles.

   Moles = Mass / Molar Mass

2. Use the Molar Ratio:

   Using the stoichiometric coefficients from the balanced chemical equation, find the moles of the desired substance.

   Moles of Desired = Moles of Given * (Coefficient of Desired / Coefficient of Given)

3. Convert Moles to Mass:

   Convert the moles of the desired substance into mass using its molar mass.

   Mass = Moles * Molar Mass

Example Calculation

Consider the reaction: 2H₂O → 2H₂ + O₂. If we start with 50g of water (H₂O) and want to find out how much oxygen (O₂) is produced:

• Mass of Given (H₂O): 50 g
• Molar Mass of Given (H₂O): 18.015 g/mol
• Coefficient of Given (H₂O): 2
• Molar Mass of Desired (O₂): 32.00 g/mol
• Coefficient of Desired (O₂): 1

1. Moles of H₂O = 50 g / 18.015 g/mol ≈ 2.775 moles
2. Moles of O₂ = 2.775 moles H₂O * (1 mole O₂ / 2 moles H₂O) = 1.3875 moles O₂
3. Mass of O₂ = 1.3875 moles * 32.00 g/mol ≈ 44.4 g