3.1.9 Rate Equations

Question 1

Define Rate of reaction.

Answer 1

Change in concentration per unit time.

Question 2

What are the units of rate?

Answer 2

mol dm-3 s-1

Question 3

Define activation energy.

Answer 3

Minimum energy required for a reaction to occur.

Question 4

How does a rate change when the concentration of a zero order species is doubled?

Answer 4

Rate would stay the same.

Question 5

How does a rate of reaction change when the concentration of a first order species is doubled?

Answer 5

Rate would also double.

Question 6

How does a rate of reaction change when the concentration of a second order species is doubled?

Answer 6

It would multiply by 4.

Question 7

What are the two experimental methods for measuring a rate of reaction.

Answer 7

Continuous monitoring method and initial rates method.

Question 8

How can a continuous monitoring practical be tracked?

Answer 8

Measure the concentration of reactants at regular time intervals.

Question 9

What graph can be plotted from a continuous monitoring practical?

Answer 9

A concentration time graph.

Question 10

How can a an initial rate be found on a concentration time graph?

Answer 10

draw a tangent at t=0 and calculate gradient.

Question 11

Which equation is used to calculate a gradient?

Answer 11

dy/dx

Question 12

Complete the missing spaces with changes in concentration, rate, and order of reaction.

Answer 12

Question 13

Complete the missing spaces with changes in concentration, rate, and order of reaction.

Answer 13

Question 14

Complete the missing spaces with changes in concentration, rate, and order of reaction.

Answer 14

Question 15

Complete the missing spaces with changes in concentration, rate, and order of reaction.

Answer 15

Question 16

Complete the missing spaces with changes in concentration, rate, and order of reaction.

Answer 16

Question 17

How is an initial rates practical carried out?

Answer 17

Vary the concentration of 1 of the reactants and measure the time taken to react the endpoint.

Question 18

How is rate of calculated the initial rates method.

Answer 18

rate = 1/t

Question 19

why is rate 1/t in the initial rates method?

Answer 19

As the concentration of the product formed at the end point of the reaction is
fixed, it
can be taken as a constant.

Question 20

What does a rate concentration graph looks like for a zero order reaction?

Answer 20

Question 21

What does a rate concentration graph looks like for a first order reaction?

Answer 21

Question 22

What does a rate concentration graph looks like for a second order reaction?

Answer 22

Question 23

During an experiment, How can the order of a reactant be changed to be come zero order?

Answer 23

Use a large excess of that reactant as the concentration change would be negligible so its concentration can be taken as constant.

Question 24

What is the rate equation if the units of k are s-1?

Answer 24

r = k [A]

Question 25

What is the rate equation if the units of k are mol -2 dm 6 s-1?

Answer 25

r = k [A]^3

Question 26

What are the units of k if the rate equation is r = k [A]

Answer 26

s-1

Question 27

What are the units of k if the rate equation is r = k [A][B][C]?

Answer 27

mol -2 dm 6 s-1

Question 28

What is the Arrhenius equation for the rate constant k?

Answer 28

Question 29

What is the natural log form of the Arrhenius equation?

Answer 29

Question 30

How does the Arrhenius equation match the general equation for a straight line?

Answer 30

Question 31

Draw a sketch of a typical Arrhenius equation graph. Include the axes, the intercept and what the gradient of the line is equal to.

Answer 31

Question 32

How do you work out the activation energy (Ea) from this graph?

Answer 32

* Gradient = negative Ea/R (Ea is ALWAYS a POSITIVE number) * Gradient x R = Ea * R has units of J mol−1 K−1 so Ea calculated from gradient will be in J mol−1 * Divide by 1000 to convert Ea to kJ mol−1