Stoichiometric relationships

Stoichiometric Foundations

Stoichiometry is the quantitative backbone of chemistry, linking the amounts of reactants consumed to products formed via mole ratios.

In a balanced equation ($aA + bB \longrightarrow cC + dD$), the coefficients $a, b, c, d$ are the stoichiometric coefficients. Mass and charge must always be conserved.

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

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

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

Yield and Concentration

Percent yield measures efficiency: $\%\;\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}}\times 100$.

Here $n$ is moles, $V$ is volume in liters, and $m_{\text{solvent}}$ is mass in kilograms.

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.