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Edexcel IAL Chemistry 13.1 Kc expressions

Put product concentrations over reactants, raise each term to its equation coefficient and omit pure solids or liquids while retaining aqueous and gaseous concentration terms.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Write Kc as product concentrations over reactant concentrations with coefficient powers.
  • Omit pure solids and liquids from heterogeneous Kc while retaining aqueous or gaseous species.

13.1—Deduce an expression for Kc , for homogeneous and heterogeneous systems, in terms of equilibrium concentrations question 1

[Maximum number: 1]

The equation for the reaction between iron and steam is shown.

3Fe( s)+4H2O( g)⇌Fe3O4( s)+4H2( g)ΔH=−151.2 kJ mol−13 \mathrm{Fe}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{Fe}_{3} \mathrm{O}_{4}(\mathrm{~s})+4 \mathrm{H}_{2}(\mathrm{~g}) \quad \Delta H=-151.2 \mathrm{~kJ} \mathrm{~mol}^{-1}

What is the equilibrium constant expression for this reaction?

A

Kc=[Fe3O4]×[H2]4[Fe]3×[H2O]4K_{\mathrm{c}}=\frac{\left[\mathrm{Fe}_{3} \mathrm{O}_{4}\right] \times\left[\mathrm{H}_{2}\right]^{4}}{[\mathrm{Fe}]^{3} \times\left[\mathrm{H}_{2} \mathrm{O}\right]^{4}}

B

Kc=[Fe3O4]×[H2]4[H2O]4K_{\mathrm{c}}=\frac{\left[\mathrm{Fe}_{3} \mathrm{O}_{4}\right] \times\left[\mathrm{H}_{2}\right]^{4}}{\left[\mathrm{H}_{2} \mathrm{O}\right]^{4}} □

C

Kc=[H2]4[Fe]3×[H2O]4K_{\mathrm{c}}=\frac{\left[\mathrm{H}_{2}\right]^{4}}{[\mathrm{Fe}]^{3} \times\left[\mathrm{H}_{2} \mathrm{O}\right]^{4}} □

D

Kc=[H2]4[H2O]4K_{\mathrm{c}}=\frac{\left[\mathrm{H}_{2}\right]^{4}}{\left[\mathrm{H}_{2} \mathrm{O}\right]^{4}}

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