Rates Of Reaction

Question 1

How are reaction rates measured?

Answer 1

Changes in the quantities of reactants or products over times

Question 2

What is the rate equation?

Answer 2

Rate = k [A]order[B]order

Question 3

What happens when you change the concentration in a reaction?

Answer 3

Changes the rate of reaction

Question 4

What is first order?

Answer 4

The concentration of a reactant is directly proportional to the rate

Question 5

What is zero order?

Answer 5

When the concentration of a reactant has no effect on the rate?

Question 6

What is second order?

Answer 6

The rate of reaction is increased by the amount that the concentration was increased squared

Question 7

What does the overall order of a reaction give?

Answer 7

The overall effect of the concentrations of all reactants on the rate of reaction

Question 8

How is the overall order calculated?

Answer 8

Overall order = sum of orders

Question 9

What are two methods of continuous Monitoring of a reaction that produces gas?

Answer 9

Monitoring by gas collection

Monitoring by mass lost

Question 10

What does a colorimeter do?

Answer 10

Measure the intensity of light passing through a sample

A filter of a complementary colour is chosen to the colour absorbed in the reaction

Question 11

Outline a reaction for determining concentration using a colorimeter

Answer 11

Prepare standard solutions of known concentrations
Zero colorimeter with water
Measure absorbance of standard solutions
Plot calibration curve - absorbance against conc
Take absorbance of unknown
Compare on calibration curve

Question 12

What is the gradient of a concentration time graph?

Answer 12

Rate of reaction

Question 13

What is half life?

Answer 13

Time taken for Half of a reactant to be used up

Question 14

Describe exponential decay

Answer 14

Constant half life with concentration halving every half life - as in first order reaction

Question 15

What are the two methods of determining the rate constant from a concentration time graph for first order reaction?

Answer 15

Calculating rate constant from the rate - tangent to curve drawn and gradient calculated giving the rate

Calculating rate constant from half life - k=ln2
—-
T1/2

Question 16

What is a clock reaction?

Answer 16

Time from start of reaction to an visual change is observed
Convenient way of obtaining initial rate by taking single measurement
Initial rate is proportional to 1/time
Repeated several times with different conc

Question 17

What is the rate determining step?

Answer 17

The slowest step in the reaction mechanism

Question 18

What is the reaction mechanism?

Answer 18

Series of steps that make up an overall reaction

Question 19

What does the rate equation only include?

Answer 19

Species involved in the rate determining step

Question 20

What do the orders in the rate equation match?

Answer 20

The number of species involved in the rate determining step

Question 21

What happens to rate and the constant as temperature increases?

Answer 21

They both increase

Question 22

What two factors contribute or the increased rate and constant when temp is increased?

Answer 22

Shifts Boltzmann distribution to right increasing proportion of particles that exceed activation energy
As temp increases particles move faster and collide more frequently

Question 23

What is stoichiometry?

Answer 23

The relative amounts of te species in the reaction

Question 24

What does the exponential factor in Arrhenius represent?

Answer 24

Proportion of molecules that exceed the activation energy