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CAIE A-Level Chemistry 7.1.5 Mole Fraction and Partial Pressure

Practise calculating mole fractions and converting them into partial pressures for gases in an equilibrium mixture.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • calculate mole fraction as moles of one gas divided by total moles of all gases in the mixture
  • calculate partial pressure as mole fraction multiplied by total pressure, keeping pressure units consistent
  • check that all mole fractions sum to one and all partial pressures sum to the stated total pressure

7.1.5—The terms mole fraction and partial pressure question 1

[Maximum number: 3]

Ammonia, NH3\mathrm{NH}_{3}, is manufactured from nitrogen and hydrogen by the Haber process.

N2( g)+3H2( g)⇌2NH3( g)ΔH=−92 kJ mol−1\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-92 \mathrm{~kJ} \mathrm{~mol}^{-1}

At a pressure of 2.00×107 Pa,1.00 mol2.00 \times 10^{7} \mathrm{~Pa}, 1.00 \mathrm{~mol} of nitrogen, N2( g)\mathrm{N}_{2}(\mathrm{~g}), was mixed with 3.00 mol of hydrogen, H2( g)\mathrm{H}_{2}(\mathrm{~g}). The final equilibrium mixture formed contained 0.300 mol of ammonia, NH3( g)\mathrm{NH}_{3}(\mathrm{~g}).

Calculate the partial pressure of ammonia, pNH3\mathrm{pNH}_{3}, in the equilibrium mixture.

Give your answer to three significant figures.

pNH3=p \mathrm{NH}_{3}=

Pa

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