AQA GCSE Chemistry

Topic Questions

6.2 Reversibility & Equilibrium

11 mark

The Haber process is an example of a reversible reaction where the forward reaction is exothermic:

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon 2NH3 (g)

What is not true about this system when it is at equilibrium?

  • The energy change of the reverse reaction is endothermic

  • The equilibrium occurs within a closed system

  • The reaction has reached completion and stopped

  • The rate of the forward reaction is equal to the rate of the reverse reaction

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21 mark

Which graph shows the highest yield of products?

  • a

  • b

  • c

  • All of the above have the same yield of products

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31 mark

The decomposition of ammonium chloride is endothermic:

NH4Cl (s) rightwards harpoon over leftwards harpoonNH3 (g) + HCl (g)

Which changes to the conditions would both decrease the amount of product in this reaction?

  Change 1 Change 2
A Increase pressure Decrease temperature
B Decrease pressure Decrease temperature
C Increase pressure Increase temperature
D Decrease pressure Increase temperature

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41 mark

The gasification of carbon is a reversible endothermic reaction:

C (s) + H2O (g) rightwards harpoon over leftwards harpoon CO (g) + H2 (g)

Which of the following conditions could be changed to increase the relative amount of H2 gas produced?

  • Increase the surface area to volume ratio of the carbon

  • Increase the pressure

  • Increase the temperature

  • Add a catalyst

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51 mark

Which statement is not true about Le Chatelier's Principle?

  • If changes to the conditions of a system are made, the system responds to counteract the change

  • If the concentration of the product is decreased, more reactants will react until an equilibrium position is reached again

  • Increasing the pressure will shift the position of the equilibrium to the side with the smaller number of molecules of gas

  • If temperature is decreased for an exothermic reaction, the relative amount of products made at the equilibrium point decreases

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61 mark

Hydrogen gas and iodine vapour can react to form hydrogen iodide:

H2 (g) + I2 (g) rightwards harpoon over leftwards harpoon 2HI (g)

Which statement is not true?

  • This reaction is reversible

  • Equal amounts of reactants and product are eventually made at equilibrium

  • This reaction can reach an equilibrium point in a closed system

  • There are equal total numbers of moles of reactant and product

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71 mark

Some systems at equilibrium can be studied by changes in colour.

Fe3+ (aq) + SCN- (aq) rightwards harpoon over leftwards harpoon FeSCN2+ (aq)

yellow     colourless                red

This reaction starts with only the reactants, and reaches equilibrium at a point where there are equal amounts of Fe3+ and FeSCN2+ present. The solutions used are very dilute.

What colour change would you expect to see during the course of the reaction?

  • Yellow to orange to red

  • Yellow to red

  • Yellow to orange

  • Yellow to red to orange

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81 mark

Which option shows two correct statements about reversible reactions and equilibrium?

  Statement 1 Statement 2
A The sign for a reversible reaction is rightwards harpoon over leftwards harpoon Reversible reactions are slower than non-reversible ones
B At equilibrium the rate of the forward reaction and the rate of the reverse reaction are equal An endothermic reaction is exothermic if reversed
C Reversible reactions are not useful in industry as they do not go to completion To reach an equilibrium the reaction must occur in a closed system
D The rate of the reaction is zero at equilibrium The concentration of the product is constant at equilibrium

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