RecallWeave / Chemistry

Which reactant
sets the limit?

Equal amounts are not always the right ratio. Make a prediction, compare what each reactant can support, and account for what remains.

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1Set up a comparison

Use 0–1000 mol, with up to three decimal places. Convert masses to moles before entering them.

Try a different starting point

Examples load the starting amounts. Compare when you are ready.

2Follow the amounts

Predict, then compare.

The smaller amount divided by its coefficient sets the shared reaction extent.

Why divide by the coefficient?

  1. Normalize each supply. In 2 H₂ + O₂ → 2 H₂O, every 2 mol H₂ supports the same reaction extent as 1 mol O₂.
  2. Use the smaller capacity. Both reactants must supply that shared extent. An excess of one cannot replace a shortage of the other.
  3. Multiply back. Extent × coefficient gives the amount consumed or formed. Starting amount − amount consumed gives the excess.
What this model assumes

Amounts of molecules are not conserved as a total count. The balanced equations conserve each kind of atom. This explorer accepts mole amounts only and does not assign measurement uncertainty.

Keep building the connection

The companion course has 12 original questions with worked explanations and transfer prompts. Save it for a RecallWeave lesson player that supports local deck import.

Background: OpenStax, Chemistry 2e, 4.3 Reaction Stoichiometry and 4.4 Reaction Yields. Examples and question wording are original; no textbook passages or figures are reproduced.