2.4 Reacting masses and volumes (of solutions and gases)

Start every stoichiometric calculation with the correct balanced equation and identify the quantity requested. Convert the supplied data to moles, apply the mole ratio from the coefficients, then convert the calculated amount into the required mass, gas volume or solution quantity.

Use the appropriate relationship and units: amount from mass uses n = m/M; solution concentration uses c = n/V with a consistent volume unit; gas volume uses the stated molar-volume conditions. Coefficients give mole ratios, not direct mass ratios, so do not apply them before the mole conversion.

For percentage yield, compare actual product with the theoretical amount: percentage yield = actual yield ÷ theoretical yield × 100. When more than one reactant is supplied, calculate the product possible from each reactant and identify the smaller amount as the limiting-reagent result; the other reactant is in excess and can be treated only after the limiting amount is established.

Finish by checking units, significant figures, the balanced atom/charge relationship, and whether the result is chemically sensible. Keep gas conditions, solution volume units, percentage-yield direction and limiting/excess labels explicit; a calculated stoichiometric relationship is a conclusion supported by these checks, not a replacement for them.