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CAIE A-Level Chemistry 7.1.8 Calculating Equilibrium Quantities

Practise using reaction stoichiometry and supplied equilibrium data to calculate remaining moles or concentrations.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • translate one known equilibrium amount into the reaction extent using balanced-equation mole ratios
  • subtract consumed reactants and add formed products to complete an initial-change-equilibrium table
  • use the resulting amounts with volume, mole fraction or total pressure data to obtain requested quantities

7.1.8—The quantities present at equilibrium question 1

[Maximum number: 2]

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 amounts, in mol, of N2( g)\mathrm{N}_{2}(\mathrm{~g}) and H2( g)\mathrm{H}_{2}(\mathrm{~g}) in the equilibrium mixture.

N2( g)=…………………………. mol H2( g)=……………………….. mol \begin{aligned} & \mathrm{N}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \text { mol } \\ & \mathrm{H}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \text { mol } \end{aligned}
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