Equilibrium constant Kp
Kp = product partial pressures / reactant partial pressures
Only gaseous species appear, and every partial pressure is raised to its equation coefficient.
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.
For N2O4(g) <=> 2NO2(g), the equilibrium partial pressures are p(N2O4) = 40 kPa and p(NO2) = 60 kPa. Calculate Kp and its unit.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Forgetting to square the NO2 partial pressure.
- Assuming Kp is unitless without cancelling pressure powers.
Exam tip: Derive the unit from total product powers minus total reactant powers after writing the expression.
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.