Rate Equations

Question 1

Define rate of reaction (1)

Answer 1

Change in concentration per unit of time

Question 2

Define activation energy (1)

Answer 2

Minimum energy required for a reaction to occur

Question 3

Why does a higher temperature increase the rate of reaction? (2)

Answer 3

At higher temperature ore particles have E greater than or equal to the activation energy
Greater frequency of successful collisions

Question 4

Why does a higher concentration/pressure increase the rate of reaction? (3)

Answer 4

More particles within the same amount of space
More collisions between particles
Greater frequency of successful collisions

Question 5

Why does breaking a solid into smaller particles increase the rate? (3)

Answer 5

Increased surface area
More collisions between particles
Greater frequency of successful collisions

Question 6

What does the term order of reaction mean? (1)

Answer 6

The power to which a species concentration is raised in the rate equation

Question 7

What is the rate equation?

Answer 7

rate = k[A][B][C]2

Question 8

If large excess of a reactant is used, what does this mean about the order of the reactant? (2)

Answer 8

Order of reaction is zero with respect to that reactant
As the reactants concentration is effectively constant

Question 9

How can the value of K (rate constant) be changed? (1)

Answer 9

If temperature is changed

Question 10

What two types of experiment determine the order of a reaction? (2)

Answer 10

Continuous monitoring method
Initial rates method

Question 11

How can the continuous monitoring method be used to measure the progress of a reaction? (2)

Answer 11

By taking samples at regular intervals
By using a visible indicator/physical property such as gas volume

Question 12

What is the problem with measuring the progress of a reaction by taking samples at regular intervals? (1)

Answer 12

Reaction mixture is still reacting

Question 13

How to solve the problem of reaction mixture still reacting when measuring the progress of a reaction by taking samples at regular intervals? (3)

Answer 13

To stop the reaction
Add a larger volume of cold distilled water
This will both cool and dilute the reaction decreasing the rate

Question 14

What is the problem with measuring the progress of a reaction by measuring the volume of gas produced at regular intervals (3)

Answer 14

Records the amount of product formed
Order of reaction is about the reactants
Volume recorded would need converting to reactant concentration

Question 15

How can the initial rates method be used to measure the progress of a reaction? (2)

Answer 15

Series of experiments are carried out
Each experiment will change the concentration of the reactant to be investigated whilst keeping all the other conditions the same

Question 16

In initial rates experiment, what is rate proportional to? (1)

Answer 16

1/time

Question 17

Method for iodine clock initial rates practical (6)

Answer 17

Measure known volumes of some reactants
Measure known volume of X (sodium thiosulfate)
Into separate containers so the reaction doesn’t start
Start the stop clock at the point of mixing (when the last of the reactants is added to the conical flask - do not add sodium thiosulfate or X last)
Stop the stop clock when the mixture turns blue/black and record
Repeat the experiment using the same total volume altering the volume of potassium iodide or A
Calculate rate = 1/time
Plot graph of 1/time against volume of potassium iodide or A

Question 18

What does the Arrhenius equation show? (1)

Answer 18

The relationship between rate constant and temperature and activation energy

Question 19

What can the Arrhenius equation be rearranged to? (1)

Answer 19

ln K = ln A - Ea/RT

Question 20

What is the rate determining step? (1)

Answer 20

The one step of a reaction which is slower than the others

Question 21

Define the term overall order of reaction (1)

Answer 21

sum of the orders of reaction of all species in the rate expression