Stoichiometry Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Stoichiometry.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The branch of chemistry that calculates the quantities of reactants and products in chemical reactions.

Using the recipe (balanced equation) to figure out how much of each ingredient you need.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Coefficients in balanced equations give the mole ratios used to convert between substances.

Common stuck point: Always start by converting to moles—then use ratios—then convert to desired units.

Worked Examples

Example 1

medium
How many grams of \text{O}_2 are needed to completely burn 16.0 g of \text{CH}_4? (\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O})

Solution

  1. 1
    Moles of \text{CH}_4 = \frac{16.0}{16.04} = 0.998\,\text{mol} \approx 1.00\,\text{mol}.
  2. 2
    From the equation: 1 mol \text{CH}_4 requires 2 mol \text{O}_2. So moles of \text{O}_2 = 2 \times 1.00 = 2.00\,\text{mol}.
  3. 3
    Mass of \text{O}_2 = 2.00 \times 32.00 = 64.0\,\text{g}.

Answer

64.0\,\text{g of O}_2
Stoichiometry uses mole ratios from balanced equations to convert between amounts of reactants and products. The steps are: grams → moles → mole ratio → moles → grams.

Example 2

hard
How many grams of \text{NH}_3 can be produced from 28.0 g of \text{N}_2 and excess \text{H}_2? (\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
How many moles of \text{H}_2\text{O} are produced when 3.0 mol of \text{H}_2 reacts with excess \text{O}_2? (2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O})

Example 2

medium
How many grams of \text{NaCl} form from 0.50 mol of \text{Cl}_2 reacting with excess sodium? (2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}; molar mass of \text{NaCl} = 58.44\,\text{g/mol})
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Background Knowledge

These ideas may be useful before you work through the harder examples.

molebalancing equationsmolar mass