Limiting Reactant & Percent Yield Cheat Sheet

Key Facts

• A balanced chemical equation is required before any stoichiometry calculation because coefficients give the mole ratios.
• Convert mass to moles using $n = \frac{m}{M}$, where $n$ is moles, $m$ is mass in grams, and $M$ is molar mass in $\text{g/mol}$.
• Use the mole ratio from the balanced equation as $\text{moles wanted} = \text{moles given} \times \frac{\text{coefficient wanted}}{\text{coefficient given}}$.
• The limiting reactant is the reactant that produces the smaller calculated amount of product.
• The excess reactant is the reactant left over after the limiting reactant is completely consumed.
• Theoretical yield is the maximum product possible from the limiting reactant under ideal conditions.
• Percent yield is calculated with $\%\text{ yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$.
• Actual yield must be less than or equal to theoretical yield in typical school laboratory calculations, so percent yield is usually $\leq 100\%$.

Vocabulary

Limiting Reactant

The reactant that is used up first and determines the maximum amount of product that can form.

Excess Reactant

The reactant that remains after the limiting reactant has been completely consumed.

Mole Ratio

A conversion factor made from coefficients in a balanced chemical equation.

Theoretical Yield

The maximum amount of product predicted by stoichiometry from the limiting reactant.

Actual Yield

The amount of product actually collected or measured in an experiment.

Percent Yield

A comparison of actual yield to theoretical yield, calculated as $\frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$.