kinetics 2

Question 1

The rate of reaction is defined as…

Answer 1

the change in concentration of a substance in unit time

Question 2

The initial rate is…

Answer 2

the rate at the start of the reaction where it is fastest

Question 3

Techniques to investigate rates of reaction (6)

Answer 3

• Measurement of the change in volume of a gas
• Measurement of change of mass
• Titrating samples of reaction mixture with acid, alkali, sodium thiosulfate etc
• Colorimetry
• Measuring change in electrical conductivity
• Measurement of optical activity

Question 4

Measurement of the change in volume of a gas

Answer 4

This works if there is a change in the number of moles of gas in the reaction.
- Using a gas syringe is a common way of following this

Question 5

Measurement of change of mass

Answer 5

This works if there is a gas produced which is allowed to escape. Works better with heavy gases such as CO2

Question 6

Titrating samples of reaction mixture with acid, alkali, sodium thiosulfate etc

Answer 6

Small samples are removed from the reaction mixture, quenched (which stops the reaction) and the titrated with a suitable reagent

Question 7

Colorimetry

Answer 7

If one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixtures

Question 8

Measuring change in electrical conductivity

Answer 8

Can be used if there is a change in the number of ions in the reaction mixture

Question 9

Measurement of optical activity.

Answer 9

If there is a change in the optical activity through the reaction this could be followed in a polarimeter

Question 10

For the following reaction, aA + bB-> products, the generalised rate equation is:

Answer 10

r = k[A]m[B]n

• r is used as symbol for rate
• The square brackets [A] means the concentration of A
• k is called the rate constant
• m, n are called reaction orders

Question 11

For zero order: the concentration of A has what effect on the rate of reaction?

r = k[A]0 = k

Answer 11

no effect on the rate of reaction

Question 12

For first order: the rate of reaction is … to the concentration of A
r = k[A]1

Answer 12

directly proportional

Question 13

For second order: the rate of reaction is… to the concentration of A squared
r = k[A]2

Answer 13

proportional

Question 14

what’s Continuous rate data?

Answer 14

This is data from one experiment where the concentration of one substance is followed throughout the experiment

Question 15

If half-lives are constant in a graph then…

Answer 15

the order is 1st order

Question 16

If half-lives rapidly increase in a graph then…

Answer 16

the order is 2nd order

Question 17

If zero order the rate stays… as the reactant is used up. This means…

Answer 17

1- constant
2- the concentration has no effect on rate.

Question 18

The value of k refers to a specific temperature and it increases if…

Answer 18

we increase temperature

Question 19

If conc is doubled and rate stays the same: order=

Answer 19

0

Question 20

If conc is doubled and rate doubles: order=

Answer 20

1

Question 21

If conc is doubled and rate quadruples : order=

Answer 21

2

Question 22

The Arrhenius equation is usually rearranged to…

Answer 22

ln k = ln A –EA/(RT)