P- Kinetics =)

Question 1

State why the Maxwell–Boltzmann curve starts at the origin. (1)

Answer 1

There are no molecules w/ no energy

Question 2

The student records the time for the cross to disappear. The cross disappears because the mixture becomes cloudy.
The student uses a stopwatch to measure the time. The stopwatch shows each time to the nearest 0.01 s
Suggest why the student records the times to the nearest second and not to the nearest 0.01 s. (1)

Answer 2

• hard to judge to nearest 0.01s

Question 3

Na2S2O3(aq) + 2 HCl(aq) → 2 NaCl(aq) + SO2(g) + S(s) + H2O(l)
Suggest, by considering the products of this reaction, why small amounts of reactants are used in this experiment. (1)

Answer 3

• SO2 formed = toxic
• limit amount formed

Question 4

Explain, in terms of collision theory, the effect of increasing the concentration of hydrogen peroxide on the rate of reaction. (2)

Answer 4

• ↑ H2O2 molecules (/ closer tgt)
• ↑ frequent successful collisions

Question 5

Define the term activation energy for a chemical reaction. (2)

Answer 5

• minimum energy
• required for a reaction to occur

Question 6

Explain why a small decrease in temperature can lead to a large decrease in the rate of a reaction. (2)

Answer 6

• a lot fewer molecules
• have energy > Ea

Question 7

Give one reason why most collisions between gas-phase reactants do not lead to a reaction. (1)

Answer 7

molecules x have enough energy

Question 8

Definition of rate of reaction. (2)

Answer 8

• change in conc.
• per unit time

Question 9

Explain why the rate of reaction between magnesium and dilute hydrochloric acid is increased much more by changing the magnesium from ribbon to powder than by doubling the concentration of the acid. (2)

Answer 9

• s.a. > doubled
• many more collisions

Question 10

Explain, in terms of collision theory, the effect of increasing the concentration of hydrogen peroxide (reactant) on the rate of reaction. (2)

Answer 10

• ↑ particles in a given vol
• ↑ freq successful collisions