Limiting reactant
compare moles / balancing coefficient for each reactant
The smaller mass is not automatically limiting; compare available moles with the equation ratio.
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
2H2 + O2 → 2H2O. A mixture contains 3.0 mol H2 and 2.0 mol O2. Identify the limiting reactant and calculate the moles of water formed.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Choosing the reactant with fewer moles without using coefficients.
- Using all of the excess reactant to calculate product.
Exam tip: Divide each mole amount by its balancing number; the smallest result identifies the limiter.
Calculations are the most trainable marks in chemistry
They come up every paper and reward a clean method. Send me one you keep dropping marks on — your first lesson is free.