3.5 - Chemical Kinetics

Question 1

What is meant by ‘rate of reaction’?

Answer 1

The change in concentration of reactants or products over time.

Question 2

What is a rate equation?

Answer 2

Question 3

What is a rate constant?

Answer 3

The constant of proportionality linking the rate of reaction and the concentrations of the reactants raised to the power of their orders in the rate equation.

Question 4

How do you calculate the units of a rate constant?

Answer 4

• Rearrange the rate equation to make k the subject.
• Substitute units into the equation.
• Cancel the common units to find the units for k.

Question 5

Answer 5

Question 6

What is meant by the term ‘order of reaction’?

Answer 6

• The order with respect to a reactant is the power to which the concentration of the reactant is raised in the rate equation.
• Overall order of a reaction = the sum of all the individual orders of the reactants.

Question 7

What do the different orders of reaction mean?

Answer 7

Question 8

What is activation energy?

Answer 8

The minimum energy required for a particular reaction to occur.

Question 9

What are some different experimental techniques that allow you to obtain rate data?

Answer 9

• Titration.
• Measuring the volume of gas released from a reaction over time.
• Measuring the change in mass of a reactant over time.
• Colorimetry.
• Measuring the time taken for a colour change.

Question 10

What are the two different method types that can be used to investigate reaction rates?

Answer 10

• Initial-rate method: Experiments are carried out where different initial concentrations of one reagent are used.
• Continuous monitoring method: The concentration/volume is continuously monitored so that a concentration or volume time graph can be produced from the data.

Question 11

What does a rate-concentration graph look like for a zero order reactant?

Answer 11

Question 12

What does a rate-concentration graph look like for a first order reactant?

Answer 12

Question 13

What does a rate-concentration graph look like for a second order reactant?

Answer 13

Question 14

What does a concentration-time graph look like for a zero order reactant?

Answer 14

Question 15

What does a concentration-time graph look like for a first order reactant?

Answer 15

Question 16

How do you calculate the rate from a first order concentration-time graph?

Answer 16

• Draw a tangent at the time you want to calculate the rate of reaction for.
• The gradient of this tangent will equal the rate of reaction.

Question 17

How do you calculate k from a zero order rate-concentration graph?

Answer 17

• Calculate the gradient of the line of best fit.
• The gradient will equal the rate constant, k.

Question 18

How do you calculate the gradient of a line/tangent?

Answer 18

Question 19

What is a rate-determining step?

Answer 19

• The slowest step of the reaction.
• Only the species that take part in the
  rate determining step (or steps that take place before it) affect the rate.

Question 20

What is the relationship between the rate-determining step and the orders with respect to the reactants?

Answer 20

• The species present in the rate equation are those that take part in the rate determining step.
• For any reactant in the rate equation, the order related to it tells you how many molecules of it are involved in the rate determining step.

Question 21

How does iodine react with propanone in acid?

Answer 21

Question 22

What equation can be used to calculate activation energy?

Answer 22

The Arrhenius equation