Stoichiometric relationships

Stoichiometry is the quantitative backbone of chemistry — it links the amounts of reactants consumed to products formed via mole ratios.

Balanced equation

$$a\,A + b\,B \;\longrightarrow\; c\,C + d\,D$$

The coefficients $a, b, c, d$ are the stoichiometric coefficients. Mass and charge must be conserved.

Conversion chain

$$\text{grams} \;\xrightarrow{\div\,M}\; \text{moles} \;\xrightarrow{\times\,\text{ratio}}\; \text{moles of target} \;\xrightarrow{\times\,M}\; \text{grams}$$

Limiting reagent — The reactant that runs out first determines the maximum yield. To find it, convert all reactants to moles and compare to the required ratio.

Concentration measures

Percent yield

$$\%\;\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}}\times 100$$

Tip: Dimensional analysis is your best friend. Track units through every step and cancel them — if the units come out wrong, the calculation is wrong.

Common pitfall: Balanced coefficients relate moles, never grams. Converting masses to moles before using the ratio — and back after — is the non-negotiable detour of every stoichiometry problem.