1. 1
   A teacher uses a computer simulation to model particles of two gases moving randomly in a sealed container, occasionally colliding with each other, to help students understand why some collisions lead to a reaction and others do not.

   (a)

   According to collision theory, what must happen before two reacting particles can react?

   [1 mark]

   • AThey must collide with sufficient energy
   • BThey must be the same size
   • CThey must both be gases
   • DThey must be at absolute zero

   (b)

   What term describes the minimum amount of energy that colliding particles must have in order to react?

   [1 mark]

   • AIonisation energy
   • BBond energy
   • CKinetic energy
   • DActivation energy

   (c)

   In the simulation, some collisions between particles result in a reaction while most do not. Explain why not every collision between reacting particles leads to a reaction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student researches two different chemical reactions occurring at room temperature: reaction X, which has a low activation energy, and reaction Y, which has a much higher activation energy.

   (a)

   A student compares two reactions: one with a low activation energy and one with a high activation energy, at the same temperature. Which reaction is expected to proceed faster?

   [1 mark]

   • ABoth proceed at exactly the same rate
   • BThe reaction with the high activation energy
   • CThe reaction with the low activation energy
   • DNeither reaction can proceed

   (b)

   Which statement best describes activation energy?

   [1 mark]

   • AThe total energy released by a reaction
   • BThe minimum energy particles must have to react when they collide
   • CThe energy needed to melt a solid
   • DThe energy released when a catalyst is added

   (c)

   Explain why reaction Y, with the higher activation energy, is expected to proceed much more slowly than reaction X at the same, fixed temperature.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student mixes two colourless solutions in a test tube, expecting a colour change to indicate a reaction, but after several minutes at room temperature no colour change is observed, even though the reactants should react according to the balanced equation given.

   (a)

   Define collision theory and state the two conditions needed for reacting particles to successfully react according to this theory.

   [3 marks]

   (b)

   Suggest two possible reasons, based on collision theory, why no reaction was observed between the two solutions, and suggest one change the student could make to increase the chance of a successful reaction occurring.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry lecturer explains to students why two different reactions, carried out under identical conditions of temperature and concentration, proceed at very different rates, using energy level diagrams to show the activation energy of each reaction.

   (a)

   Using collision theory, explain fully why chemical reactions require both collisions between particles and a minimum amount of energy in order to proceed, and describe how this explains why reactions occur at different rates under otherwise similar conditions.

   [6 marks]

   (b)

   The lecturer then raises the temperature of both reactions by the same amount. Explain, using collision theory and the idea of activation energy, why raising the temperature increases the rate of both reactions, and discuss whether you would expect this increase in rate to affect the reaction with the higher activation energy more, less, or the same as the reaction with the lower activation energy.

   [6 marks]

   Total for question 4: 12 marks

End of questions