Kinetics (DONE)

Question 1

How is rate calculated?

Answer 1

Change in concentration/mass/volume DIVIDE BY change in time

Question 2

Describe five common methods for measuring rate

Answer 2

• Colorimetry. Change in the amount of a coloured substance/absorbance
• Gas volume. Gas syringe to measure volume of gas produced
• Mass. Weighing scale to measure the mass of gas released
• Pressure. Pressure gauge to measure change in pressure
• Sample, quench, titrate/ Sample samples of the reaction are removed at regular time intervals and immediately quenched to stop reaction by putting them into an ice bath. The sample is then titrated

Question 3

What is the definition of the order of reaction?

Answer 3

The power to which the concentration of a particular reactant is raised in an experimentally determined rate equation

Question 4

What are the units of k in the following:
- Zero order reactions
- First order reactions
- Second order reactions

Answer 4

1. k = mol dm⁻³ s⁻¹
2. k = s⁻¹
3. k = mol⁻¹ dm³ s⁻¹

Question 5

Describe the rate-concentration graphs of the following:
- Zero order reactions
- First order reactions
- Second order reactions

Answer 5

1. Remains constant
2. Straight line passing through the origin with a gradient of k (directly proportional)
3. Increasing slope rapidly due to rate being proportional to concentration squared

Question 6

What is the rate determining step?
(2 marks)

Answer 6

• Controls the rate of reaction
• Usually the slowest step (1st step usually)

Question 7

What does Arrhenius equation show?

Answer 7

The effect that changing the temperature/adding a catalyst to lower the activation energy has on the rate constant

Question 8

State the Arrhenius equation and then describe what each component means.

Answer 8

k = Ae⁻ᴱᵃ/ᴿᵀ
k is the rate constant
A is the frequency factor
Ea is the activation energy in J mol⁻¹
R is the gas constant
T is the temperature in Kelvin