Stoichiometry: reading an equation as a ratio
Coefficients in a balanced equation express ratios between amounts of substance. They connect moles of reactants and products.
The essential idea
Coefficients in a balanced equation express ratios between amounts of substance. They connect moles of reactants and products.
Example
In 2 H₂ + O₂ → 2 H₂O, two moles of H₂ react with one mole of O₂ to form two moles of H₂O in the idealized model.
Mini problem
If you have 4 mol H₂ and enough O₂, how many moles of water can form?
Show the solution
The H₂:H₂O ratio is 2:2, so 4 mol H₂ can form 4 mol H₂O.
Common mistake
Do not replace reasoning with a memorized rule. Always check geometry, units, coefficients or model assumptions.
Guided exercise
In 2 H₂ + O₂ → 2 H₂O, how many moles of O₂ are needed to consume 6 mol H₂?
Show the detailed solution
The H₂:O₂ ratio is 2:1. Therefore 6 mol H₂ require 3 mol O₂.
Avoid this
Coefficients give amount-of-substance ratios, not grams directly.