4.1.3—Ideal gas equation pV = nRT
- Syllabus
- 9701–2028–2029
- Objective
- 4.1.3
- Level
- AS
Use pV = nRT only with consistent units and the correct amount of gas
Use the ideal-gas equation pV = nRT to connect pressure, volume, amount of gas and temperature. Identify the unknown and keep pressure, volume, amount and temperature consistent with the units required by the chosen gas constant.
Before substituting, convert pressure to Pa, volume to m³ and temperature to kelvin; keep the amount in mol. A value in kPa, cm³ or dm³ is not ready for direct use with the SI value of R, and Celsius must not be used as an absolute temperature.
Use an ordered calculation: write pV = nRT, rearrange for the unknown, audit units, substitute, calculate, and convert the final output only when needed. For molar mass, first find the amount from n = pV/RT, then divide mass by amount in moles.
Do not mix pressure, volume or temperature units, confuse mass with amount of substance, or use the wrong amount of gas. Keep this card on quantitative use of the ideal-gas equation; deviations from ideal behaviour belong to the neighbouring model-and-limitations objective.
ConceptA-Level CAIE Chemistry AS