5.2 rate of reaction - exam questions

Question 1

Why the rate of reaction increases as the temperature increases? (3)

Answer 1

• Idea that acid particles move faster / particles have more energy
• Idea of increased collision frequency (between acid and thiosulfate)
• Idea of more successful collisions / collisions (between acid and thiosulfate) are more energetic / more particles have the activation energy

Question 2

Silicon dioxide is used as a catalyst.
Suggest why 1g of silicon dioxide is more effective as a catalyst when used as nanoparticles rather than as a powder. (3)

Answer 2

• (Silicon dioxide) nanoparticles have a greater surface area (to volume ratio than powder)
• Idea that chemical reactions take place on the surface of a catalyst
• Idea that there will be more (frequent) collisions / the rate of reaction will be faster

Question 3

How higher concentration affects rate of reaction (2)

Answer 3

• acid particles are more crowded in experiment / acid particles are closer together / more acid particles per unit volume / more acid particles per cm3 / more acid particles in the same space
• more (successful) collisions per second / collisions more often / increased collision frequency / more chance of a collision

IGNORE references to ‘faster’ collisions

Question 4

The student repeats experiment 1. This time he uses acid at a higher temperature.Explain, using the reacting particle model, what happens to the rate of reaction. (3)

Answer 4

• idea that acid particles move faster / particles have more energy
• idea of increased collision frequency
• idea of more successful collisions / collisions are more energetic

Question 5

The rate of reaction between marble and hydrochloric acid can be decreased by:
• Using a more dilute solution of hydrochloric acid
• Cooling the acid.
Explain how each of these methods make the reaction slower.
Use ideas about collisions between particles. (4)

Answer 5

More dilute acid:

• idea of less crowded acid particles / less acid particles in same volume
• idea of reduced collision frequency (between acid and calcium carbonate)

Decreasing the temperature of the acid:

• idea that acid particles move slower / particles have less energy
• idea of reduced collision frequency (between acid and calcium carbonate)
• idea of less successful collisions / collisions between marble chips and acid are less energetic