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Mendeleev · Chemistry pathway · level 2

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.

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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.

Go further

StoichiometryExplore tools
Method

Stoichiometry in four questions

Balance the equation, convert to moles, apply the coefficient ratio, then convert to the requested unit.

Key idea

Stoichiometry: reading an equation as a ratio

Key idea

Stoichiometry: reading an equation as a ratio

n = m/M

Coefficients in a balanced equation express ratios between amounts of substance. They connect moles of reactants and products.

Guided example

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.

Put it into practice

Stoichiometry: reading an equation as a ratio

Choose a concrete case linked to Stoichiometry: reading an equation as a ratio. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.

Check your answer

A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.

Periodic table