Quantitative calculation of reactants and products using mole ratios from balanced equations.
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Stoichiometry uses the mole ratios given by the coefficients in a balanced equation to calculate quantities of reactants and products. The reliable path is to convert the known quantity to moles, apply the mole ratio to find moles of the desired species, and then convert to mass, volume or concentration. Molar masses link grams to moles, and for gases the ideal gas law or molar volume at standard conditions links volume to moles. These calculations assume the reaction goes to completion as written and that reagents are present in the equation's ratio. The theoretical amounts computed this way set the upper limit against which actual yields are compared. Most errors arise from skipping the mole conversion step.
Key ideas: Use the road map grams A to moles A to moles B to grams B, with mole ratio from coefficients as the bridge. For solutions use moles = M x V, and for gases at STP use 22.4 L/mol (0 C and 1 atm) or PV = nRT. Express the ratio as a fraction with the wanted species on top. Always start with a balanced equation and keep units visible.
Common mistakes and connections: Typical errors are using the mass ratio instead of the mole ratio, using unbalanced coefficients, and applying 22.4 L/mol at room temperature (24.5 L/mol at 25 C). Students also forget that the amounts are limited by the scarcer reactant. Related to limiting reagent, percent yield, titration calculations and gravimetric factors.
Using 2 H2 + O2 giving 2 H2O, 10 g of hydrogen is 4.96 mol and needs 2.48 mol O2 (79.4 g), forming 89.4 g of water; masses balance. The interactive lesson shows this as a live animation or chart.
Burning 10 g of hydrogen requires about 79 g of oxygen and forms about 89 g of water.
Quantitative calculation of reactants and products using mole ratios from balanced equations.
Stoichiometry is a beginner topic in Analytical, Lab & Spectroscopy. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Analytical, Lab & Spectroscopy first: Empirical Formula, Molecular Formula, Balancing Equations.
The next topics in Analytical, Lab & Spectroscopy are Limiting Reagent and Theoretical and Percent Yield.
Yes. The interactive lesson includes a self-check question on Stoichiometry, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Stoichiometry is topic 14 of 99 in Analytical, Lab & Spectroscopy.