1: Reaction Kinetics

Question 1

What does kinetics mean

Answer 1

Things related to the rate of a reaction

Question 2

What is rate of reaction

Answer 2

The rate of change of concentration of a reaction or product with time

Question 3

What are the units for rate for reaction

Answer 3

moldm¯³s¯¹ (or per min etc)

Question 4

How can you find the rate of reaction from a concentration against time graph

Answer 4

Draw a tangent to the curve and calculate the gradient

Question 5

Examples of continuous monitoring

Answer 5

• Mass may be monitored, where the change is due to loss of a gas to the atmosphere.
• A gas evolved in a reaction may be collected.
• pH can be monitored using a pH meter
• If there is a colour change in a reaction, colorimetry can be used.

Question 6

How does a colourimeter work

Answer 6

A colorimeter uses a filter to select light in a wavelength range where there is a big difference in
the strength of absorption by the products compared to the reactants (eg strong absorption by
one and zero by the other). This light is passed through the sample and its intensity detected on
the other side

Question 7

What is the rate equation

Answer 7

The rate equation for a reaction is an equation showing how the rate depends on the concentration of reactions

Question 8

What is a generic rate equation

Answer 8

Rate = K[A]^m [B]^n

Question 9

What is the overall order of a reaction

Answer 9

The sum of the separate orders of reaction

Question 10

Why can’t the orders of reaction be deduced from the reaction equation

Answer 10

Because it depends on the mechanism of the reaction

Question 11

What is k in the rate equation

Answer 11

The rate constant

Question 12

How is the rate constant affected by the temperature and why

Answer 12

k increases as the temperature increases as the proportion of reactant molecules (or ions) with energy greater than the activation energy increases

Question 13

Does pressure affect the rate constant

Answer 13

no

Question 14

How does a catalyst change the rate equation

Answer 14

The whole rate equation changes as there is a new pathway with lower activation energy.

Question 15

What is a general formula for finding the units the rate constant

Answer 15

mol^(1-x) dm^(3x-3) s¯¹

where x is the overall order of the reaction

Question 16

What is the half life of a reaction

Answer 16

The time taken for the concentration of a reactant to fall to half of its original value

Question 17

What the rate equation for a zero order reaction

Answer 17

rate = k

Question 18

Units for the rate constant in a 0 order reaction

Answer 18

moldm¯³s¯¹

Question 19

What does the graph look like for concentration v time for zero order reaction

Answer 19

A straight line with negative gradient

Question 20

What does the rate v concentration graph look like for zero order reaction

Answer 20

Straight (horizontal) line with 0 gradient

eg. y=5

Question 21

What is the trend for successive half lives for zero order reactions

Answer 21

Successive half lives decrease (half)

Question 22

What is the rate equation for first order reaction with respect to A

Answer 22

Rate = k[A]

Question 23

What does the concentration v time graph look like for a first order reaction

Answer 23

Curved line of negative gradient

Like the positive part of 1/x

Question 24

What is the trend for successive half lives for a 1st order reaction

Answer 24

Successive half lives are constant

Question 25

Units for rate constant for 1st order reaction

Answer 25

s¯¹

Question 26

Equation for calculating half life for a 1st order reaction

Answer 26

t½= ln2 / k

Question 27

What does the rate v concentration graph look like for 1st order reaction

Answer 27

Rate is directly proportional to concentration (y=x)

Question 28

What is the rate equation for a second order reaction with respect to A

Answer 28

Rate = k[A]²

Question 29

What does the concentration v time graph look like for second order reactions

Answer 29

Curve with negative gradient

Question 30

What is the trend for successive half lives for a second order reaction

Answer 30

Successive half lives increase

Question 31

What does the rate v concentration graph look like for second order reaction

Answer 31

Curve with positive gradient (similar to the positive part of y=x²)