Stoichiometry (Moles ↔ Mass)
Chemistry
Intro: Convert given mass to moles, apply stoichiometric ratio, convert to target mass.
Worked example
- 2H2 + O2 → 2H2O; given 4.0 g H2; find mass H2O
- Balanced: $2\mathrm{H_2}+\mathrm{O_2}\to2\mathrm{H_2O}$.
- Molar masses: $M_{\mathrm{H_2}}\approx2.016$, $M_{\mathrm{H_2O}}\approx18.015\,\mathrm{g/mol}$.
- Convert given: $n(\mathrm{H_2})=\dfrac{4.0\,\mathrm{g}}{2.016\,\mathrm{g/mol}}=1.984\,\mathrm{mol}$.
- Mole ratio $\mathrm{H_2:H_2O}=2:2\Rightarrow n(\mathrm{H_2O})=1.984\,\mathrm{mol}$.
- Mass target: $m(\mathrm{H_2O})=nM=1.984\cdot18.015=35.72\,\mathrm{g}\approx35.7\,\mathrm{g}$.
- Answer: $\boxed{35.7\,\text{g H2O}}$.
FAQs
Limiting reactant?
For multiple reactants, we detect the limiting reagent automatically.
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