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Edexcel IAL Chemistry 9.9 Reversible reactions and dynamic equilibrium

State both defining conditions without claiming reactions stop or concentrations are equal, then use rate, concentration or mole data to test equilibrium conclusions.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Define dynamic equilibrium as equal opposing rates with constant concentrations.
  • Interpret rate or concentration graphs to identify when equilibrium has been reached.
  • Use balanced-equation changes to calculate amounts in an equilibrium mixture.

9.10—Predict and justify the qualitative effects of changes of temperature, pressure and concentration on the position question 1

[Maximum number: 2]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question 9.10—Predict and justify the qualitative effects of changes of temperature, pressure and concentration on the position question 1 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

Ethanol can be manufactured by reacting ethene with steam.

C2H4( g)+H2O( g)⇌C2H5OH( g)ΔrH=−45 kJ mol−1\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{~g}) \quad \Delta_{\mathrm{r}} H=-45 \mathrm{~kJ} \mathrm{~mol}^{-1}

This reaction is usually carried out in industry at 300∘C300^{\circ} \mathrm{C} and 70 atm pressure using a catalyst.

Explain the effect on the equilibrium position and the equilibrium yield of ethanol if the reaction is carried out at 300∘C300^{\circ} \mathrm{C} and 200 atm pressure.

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