Question

You want to find the actual amount of reactants that are needed to get a desired amount of product.

Which information is required?

Responses

heat the reaction generates

heat the reaction generates

percent yield

percent yield

excess reactant

excess reactant

unbalanced equation for that reaction

Answer 1

To calculate how much reactant you must actually use to make a desired amount of product you need:

- A balanced chemical equation (stoichiometric coefficients). An unbalanced equation is not sufficient.
- The desired amount of product (mass or moles).
- The molar masses of reactants and product (to convert between mass and moles).
- The percent yield (if the reaction does not go to 100% — used to increase the theoretical amount to the actual amount to charge).
- Information about which reactant(s) will be in excess or limiting, if that is part of the situation (you must know which reagent limits the reaction or whether you intend to use an excess).

You do NOT need the heat the reaction generates to compute reactant amounts.

Quick calculation steps:
1. Convert desired product mass → moles (mol = mass / M).
2. Use balanced equation to get theoretical moles of each reactant (mol_reactant = mol_product × stoich_coeff_reactant / stoich_coeff_product).
3. If percent yield < 100%, divide the theoretical moles of reactant by (percent_yield/100) to get the actual moles required.
4. Convert moles of reactant → mass (mass = moles × M).

If a limiting reagent or planned excess is involved, account for that when choosing which reactant amount to calculate or adjust.