GCSEScienceOCRCombined Science A (Gateway)ChemistryExam QuestionsMonitoring & Controlling Chemical ReactionsEquilibria

Equilibria (OCR GCSE Combined Science A (Gateway): Chemistry): Exam Questions

Exam code: J250

32 mins20 questions

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Equilibria

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11 mark

Look at the equation for the Haber process.

N2 + 3H2 ⇌ 2NH3

What is meant by the symbol ⇌ in the equation?

  • A reaction that involves a catalyst.

  • A reaction that is exothermic

  • A reaction with 100% atom economy.

  • A reversible reaction.

Choose your answer

21 mark

Which statement is true for a reversible reaction when it is at dynamic equilibrium?

  • The concentration of the products is increasing.

  • The rate of the backward reaction is greater than the rate of the forward reaction.

  • The rate of the forward reaction is equal to the rate of the backward reaction.

  • The rate of the forward reaction is greater than the rate of the backward reaction.

Choose your answer

31 mark

Ammonia is made in the Haber process.

N2 + 3H2 rightwards harpoon over leftwards harpoon 2NH3

What happens when this reaction reaches equilibrium?

  • The backward reaction happens at a faster rate than the forward reaction.

  • The forward and backward reactions happen at the same rate.

  • The forward and backward reactions stop happening.

  • The forward reaction happens at a faster rate than the backwards reaction.

Choose your answer

41 mark

The diagram shows a test tube containing ammonium chloride that has been heated gently. 

Diagram of a tilted test tube with ammonium chloride at the bottom, labelled X and Y indicating two layers of substance inside, in shades of grey.

Which two gases are present at position Y? 

  • ammonia and hydrogen chloride.

  • ammonia and chlorine

  • hydrogen and chlorine

  • ammonia and hydrogen

Choose your answer

51 mark

When hydrogen gas is heated with iodine gas, hydrogen iodide gas is produced.

The equation for this reversible reaction is:

hydrogen  +  iodine  ⇌  hydrogen iodide

This reversible reaction reaches equilibrium in a sealed container. 

Which of the following statements is correct?

  • The forward reaction and reverse reaction are both exothermic.

  • The mass of each substance does not change.

  • The hydrogen no longer reacts with iodine.

  • The gases have escaped from the container.

Choose your answer

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

Choose your answer

21 mark

Which graph shows the highest yield of products?

  • P1-dWbBs_6-2-mcq-q2a
  • 6-2-mcq-q2b
  • 6-2-mcq-q2c

  • All of the above have the same yield of products

Choose your answer

31 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

Choose your answer

41 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

Choose your answer

51 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 as of product

Choose your answer

61 mark

Some systems at equilibrium can be studies 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

Choose your answer

71 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

    Choose your answer

    81 mark

    Which statement describes what happens when a reaction reaches equilibrium?

    • The forward reaction happens at a faster rate than the backwards reaction.

    • The forward and backward reactions happen at the same rate.

    • The forward and backward reactions stop happening.

    • The backward reaction happens at a faster rate than the forward reaction.

    Choose your answer

    11 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

      Choose your answer

      21 mark

      Higher Only

      Look at the equation for a reversible reaction.

      4NH3 (g) + 5O2 (g) ⇌ 4NO (g) + 6H2O (g)    ΔH = –950 kJ mol–1

      The reversible reaction forms a dynamic equilibrium in a sealed container.

      Which of the following would move the position of equilibrium to the right?

      • Decreasing the pressure and decreasing the temperature

      • Increasing the pressure and decreasing the temperature.

      • Increasing the pressure and increasing the temperature.

      • Increasing the pressure and using a catalyst.

      Choose your answer

      31 mark

      Which graph shows a dynamic equilibrium?

      • screenshot-2024-11-06-214536
      • screenshot-2024-11-06-214635
      • screenshot-2024-11-06-214753
      • screenshot-2024-11-06-214835

      Choose your answer

      41 mark

      The reaction for the production of ammonia is shown below.

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

      What is the effect of increasing pressure on the rate of production of ammonia and the percentage yield of ammonia?

       

      rate of production

      percentage yield

      A

      increases

      decreases

      B

      increases

      increases

      C

      decreases

      increases

      D

      decreases

      decreases

        Choose your answer

        51 mark

        Carbon monoxide and steam react together exothermically to produce the alcohol methanol, as shown in the equation.

        CO(g) + 2H2(g) ⇌ CH3OH(g)

        Both reactants and the product are gaseous. Which conditions of pressure and temperature would provide the highest yield of CH3OH?

        • Low pressure and low temperature.

        • Low pressure and high temperature.

        • High pressure and low temperature.

        • High pressure and high temperature.

        Choose your answer