Collision theory and activation energyIB MYP Chemistry: Subtopic test

1. 1
   A class in Kuala Lumpur uses a model in which students walk around a hall as particles. Pairs of students sometimes collide, but only some of the collisions are counted as a reaction.

   (a)

   What name is given to the minimum energy that colliding particles must have in order to react?

   [1 mark]

   • AKinetic energy
   • BActivation energy
   • CBond energy
   • DThermal energy

   (b)

   Two particles collide but do not react. What is the most likely reason?

   [1 mark]

   • AThey collided with less than the activation energy
   • BThey were at too low a concentration
   • CThey were catalysts
   • DThey had too much energy

   (c)

   State two conditions that must be met for a collision between particles to be successful.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pupil in Chennai reacts magnesium ribbon with dilute hydrochloric acid. She then repeats the experiment with a more concentrated acid, and later with the original acid warmed to a higher temperature.

   (a)

   What effect does using the more concentrated acid have on the collisions?

   [1 mark]

   • AEach acid particle has more energy
   • BThe collisions are less frequent
   • CThere are more acid particles in the same volume, so collisions are more frequent
   • DThe activation energy falls

   (b)

   What is the main reason that warming the acid greatly increases the rate?

   [1 mark]

   • AThe activation energy becomes lower
   • BThe acid particles become more concentrated
   • CThe magnesium has a larger surface area
   • DA greater proportion of collisions have energy equal to or greater than the activation energy

   (c)

   Explain, using ideas about collisions, why the rate of this reaction falls as it proceeds.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A brewery in Dublin uses yeast to convert sugar into ethanol and carbon dioxide at about 30 °C. Yeast cells contain enzymes. The company's chemical plant next door makes other products using metal catalysts.

   (a)

   Explain how a catalyst increases the rate of a reaction.

   [3 marks]

   (b)

   Describe what an enzyme is, give two features of how enzymes work, and explain why the brewery keeps the temperature at about 30 °C and not at 80 °C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the Haber process, nitrogen reacts with hydrogen to make ammonia, which is used to make fertilisers. At a pilot plant in Trinidad, engineers measured how long it took to make 100 kg of ammonia at the same temperature and pressure. Without a catalyst it took 80 minutes, and with an iron catalyst it took 20 minutes. One engineer's hypothesis was that the iron catalyst would increase the rate because it lowers the activation energy. Each result came from a single trial.

   (a)

   Process the data and evaluate the engineer's hypothesis using ideas about collisions. Comment on the reliability of the trial.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of producing ammonia for fertilisers on a large scale, and evaluate whether it is justified.

   [6 marks]

   Total for question 4: 12 marks

End of questions