The ideal gas equation
pV = nRT (p in Pa, V in m3, T in K, R = 8.31 J/K/mol)
pV = nRT only works in SI units — pascals, cubic metres and kelvin — so convert first.
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.
Calculate the volume, in dm3, occupied by 0.50 mol of an ideal gas at a temperature of 298 K and a pressure of 100 kPa. (R = 8.31 J/K/mol)
Do the calculation on paper first — then mark it.
Where the marks get lost
- Leaving pressure in kPa or volume in cm3/dm3 — everything must be in SI (Pa, m3, K) before substituting.
- Forgetting temperature must be in kelvin (add 273 to a Celsius value).
- Not converting the final volume from m3 back to dm3 (x1000) or cm3 (x1 000 000).
Exam tip: Convert every quantity to SI on your first line: Pa, m3, K. Then the volume comes out in m3 and you multiply by 1000 for dm3 at the very end.
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.