1. 1
   A quarry worker is investigating how quickly limestone reacts with dilute hydrochloric acid under different conditions, comparing large rock chunks with crushed limestone chips, and later comparing the crushed chips reacting with acid of different concentrations.

   (a)

   A quarry worker crushes large limestone rocks into smaller chips before reacting them with dilute hydrochloric acid, and notices the reaction happens faster than with the large rocks. In terms of collision theory, why does crushing the limestone increase the rate of reaction?

   [1 mark]

   • AIt decreases the surface area, reducing collisions
   • BIt increases the surface area, increasing the frequency of collisions
   • CIt increases the activation energy of the reaction
   • DIt reduces the concentration of the acid

   (b)

   The quarry worker then repeats the experiment using crushed limestone chips but with a more concentrated hydrochloric acid solution. In terms of collision theory, why does increasing the acid concentration increase the rate of reaction?

   [1 mark]

   • AThere are more acid particles in the same volume, increasing collision frequency
   • BThe particles move more slowly
   • CThe activation energy is lowered
   • DThe surface area of the limestone increases

   (c)

   Describe an experiment the quarry worker could carry out to investigate the effect of surface area of marble chips on the rate of reaction with hydrochloric acid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chef is comparing how quickly food cooks in a pressure cooker, which increases both temperature and pressure inside a sealed pot, compared with cooking the same food in an open pan of boiling water at normal atmospheric pressure, and wants to understand the chemistry behind the faster cooking.

   (a)

   A chef notices that food cooks faster in a pressure cooker than in an open pan of boiling water. Considering the effect of temperature on reaction rate, which statement best explains why increasing temperature increases the rate of the cooking reactions?

   [1 mark]

   • AThe surface area of the food decreases
   • BParticles move more slowly, reducing collisions
   • CThe concentration of reactants decreases
   • DParticles move faster and collide more frequently and with more energy

   (b)

   For gas-phase reactions specifically (not the cooking example), increasing the pressure of a reacting gas has a similar effect to increasing which other factor?

   [1 mark]

   • ATemperature
   • BCatalyst activity
   • CConcentration
   • DActivation energy

   (c)

   Explain, in terms of particle collision theory, why increasing pressure increases the rate of a reaction involving gases.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A car manufacturer is testing the effectiveness of a new platinum catalyst used in catalytic converters, which speed up the conversion of harmful exhaust gases into less harmful ones, and a research chemist wants to represent and explain this catalytic effect using a reaction profile diagram.

   (a)

   A car manufacturer uses a platinum catalyst in a catalytic converter to speed up reactions that remove harmful exhaust gases. Explain what is meant by a catalyst, and describe how a catalyst increases the rate of a reaction without being used up.

   [3 marks]

   (b)

   Describe, in words, how a reaction profile diagram for the catalysed reaction would differ from one for the same uncatalysed reaction, referring to activation energy and the overall enthalpy change (ΔH).

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school laboratory technician is designing a practical investigation for students on the catalytic decomposition of hydrogen peroxide solution, comparing how the physical form of a solid catalyst (such as powder versus granules) affects the rate of oxygen gas production, before the investigation is trialled with a class.

   (a)

   A school laboratory technician is preparing an investigation for students into how surface area affects the rate of the catalytic decomposition of hydrogen peroxide solution using different solid catalysts. Describe, in full detail, an experiment the technician could design to investigate the effect of using different solid catalysts (in different physical forms, such as powder versus granules) on the rate of decomposition of hydrogen peroxide solution, including how the rate of reaction would be measured.

   [6 marks]

   (b)

   After trialling the experiment, the technician finds that using powdered catalyst produces gas noticeably faster at first, but the total volume of gas collected by the end is the same for both the powder and the granules. Explain, in terms of collision theory and the role of a catalyst, why the initial rate differs between the two catalyst forms but the total volume of gas produced is the same, and evaluate why comparing gradients rather than only final volumes is important in this investigation.

   [6 marks]

   Total for question 4: 12 marks

End of questions