Rate Equations

Question 1

Define the term rate of reaction

Answer 1

Change in concentration of any product or reactant per unit time

Question 2

At a given instant, how could you calculate the rate of a reaction

Answer 2

Change in concentration divided by change in time

Question 3

How could you measure the rate of reaction experimentally

Answer 3

Use a colorimeter at suitable intervals if there is a colour change
If gas is evolved, use a gas syringe to collect volume if gas evolved, or measure the change in mass of the reaction mixture

Question 4

How would you measure the rate of reaction for a really fast reaction

Answer 4

Use a flash of light to break bonds, use probe flashes to record amount of light absorbed by a species, this can show its concentration

Question 5

How can you determine the rate constant and rate expression for a reaction

Answer 5

Only experimentally

Question 6

What affects the value of the rate constant for a given reaction

Answer 6

Temperature

Question 7

Generic rate expression

Answer 7

Rate = k [X]^x [Y]^y

Question 8

Do species need to be in the chemical equation to be in the rate expression

Answer 8

No

Question 9

Define the term order of a reaction with respect to a given product

Answer 9

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

Question 10

Define the term overall order of reaction

Answer 10

The sum of the orders of reaction of all species I the rate expression, total order

Question 11

How would you draw a rate concentration graph

Answer 11

Plot [A] against time, draw tangents at different values

Draw a secondary graph of rate against [A]

Question 12

Rate concentration graph for a zero order reactant

Answer 12

|
|————
|_________

Question 13

Rate concentration graph for a first order reactant

Answer 13

/
| /
|/_________

Question 14

How could you confirm that a reactant is second order

Answer 14

Graph of rate against concentration squared would be a straight line through the origin

Question 15

How could you fine the rate expression using the initial rate method

Answer 15

Do a series of experiments, during which you vary concentrations so the concentrations of just one reactant changes each time
Plot a graph, draw a tangent at t=0 to find the initial rate
Compare rates and concentrations between each experiment to find order of reactants and overall rate equation

Question 16

What must you add to react with the I2 as it is produced for an iodine clock reaction

Answer 16

Known moles of sodium thiosulfate and a little starch

Reacts with I2 in 1:2 ratio

Question 17

When does the starch turn a blue black in an iodine clock reaction and why

Answer 17

When all of the Na2S2O3 has been used up and so I2 is produced, which reacts with starch leading to a blue black colour

Question 18

How can you calculate the rate of reaction from the data from an iodine clock reaction

Answer 18

Record time taken for colour change to occur

Use rate = 1/t

Question 19

What is the effect of a 10k temperature increase on the rate of reaction

Answer 19

Double rate of reaction

Question 20

What is true of the half life of a first order reactant

Answer 20

Half life is constant

Question 21

What is the Arrhenius equation

Answer 21

k = Ae^-Ea/RT

Question 22

How can you convert the Arrhenius equation into a useful form

Answer 22

K = -Ea/RT + ln A

Question 23

What is the rate determining step

Answer 23

The slowest step in a reaction mechanism, which determines the overall rate of reaction