F. Kinetics

Question 1

What is collision theory

Answer 1

Reactions can only occur when collisions take place between particles with sufficient energy (activation energy)

Question 2

Name all the factors that affect the rate of reaction

Answer 2

• temperature
• concentration of a solution
• pressure of a gas reaction
• surface area of solid reactants
• using a catalyst

Question 3

What is activation energy

Answer 3

The minimum energy that a particle needs in order to react or the enthalpy change between the reactants and the transition state

Question 4

What is the transition state

Answer 4

The species that exists at the top of the curve of an enthalpy diagram

Question 5

What does the Maxwell-Boltzmann distribution show

Answer 5

The distribution of energy amongst the particles. It shows:

• no particles have zero energy
• most particles have intermediate energies
• a few have very high energies (there is no upper limit)

Question 6

Why does the Maxwell-Boltzmann distribution go through the origin

Answer 6

All particles have energy/ no particles have no energy

Question 7

Why does the Maxwell-Boltzmann distribution never touch the x-axis after it goes through the origin

Answer 7

There is always a probability that a particle has any energy even a very high one

Question 8

Describe the effect of temperature on a Maxwell-Boltzmann curve

Answer 8

• curve shifts to the right
• number of particles with very high energy increases
• total area under the curve remains the same
• number of particles with Ea increases

Question 9

What are catalysts

Answer 9

A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount

Question 10

How do catalysts work

Answer 10

They provide a different reaction pathway with a lower activation energy

Question 11

Describe the effect of a catalyst on a Maxwell-Boltzmann curve

Answer 11

It moves the position of the Ea down the x-axis on the graph

Question 12

Describe a catalytic converter

Answer 12

a honeycomb, made of a ceramic material, coated with platinum and rhodium metals (the catalysts). honeycomb to increase surface area.

Question 13

Describe 2 catalytic converters reactions

Answer 13

carbon monoxide +nitrogen oxides——> nitrogen and carbon dioxide

hydrocarbons + nitrogen oxides——> nitrogen +carbon dioxide + water

Question 14

Describe the steps of the reaction that take place on the catalytic converter

Answer 14

1. adsorption - gases form weak bonds with metals atoms of the catalyst. The gases react on the surface.
2. desorption- the products break away from the metal atoms.

Question 15

What is the rate of a reaction

Answer 15

The change in concentration per unit time

Question 16

What is the rate expression for A + B —-> C

Answer 16

rate= [A]^m[B]^n

m and n are the orders of the reaction

Question 17

What is the overall order for the reaction for a reaction with the rate equation rate= [A]^m[B]^n

Answer 17

m + n

Question 18

What is the unit for the rate constant for a 0 order reaction

Answer 18

rate = k

moldm^-3 s^-1

Question 19

What is the unit for the rate constant for a 1 order reaction

Answer 19

rate = [A]

s^-1

Question 20

What is the unit for the rate constant for a 2 order reaction

Answer 20

rate = k[B][C]

mol^-1 dm^3 s^-1

Question 21

What is the unit for the rate constant for a 3 order reaction

Answer 21

rate = [D][E]^2

mol^-2 dm^6 s^-1

Question 22

What does a graph of rate v [A] look like is As order is 0

Answer 22

Horizontal line as the concentration of A doesn’t effect the rate

Question 23

What does a graph of rate v [A] look like is As order is 1

Answer 23

Directly proportional line as rate=[A]^1

Question 24

What does a graph of rate v [A] look like is As order is 2

Answer 24

Exponential line as rate=[A]^2

Question 25

What is the initial rate method

Answer 25

• a series of experiments each with different starting concentrations
• concentration vs time graph plotted
• tangent is drawn at t=0
• by drawing initial rate the conc. of all substances in the reaction mixture are known

Question 26

What does the effect of an increase of temperature have on k

Answer 26

Increases

Question 27

What does e^(-Ea/RT) show

Answer 27

The fraction of molecules with energy greater than the activation energy

• Ea is activation energy in Jmol-1
• R is gas constant
• T is temperature in K

Question 28

What is the Arrhenius equation

Answer 28

k=Ae^(-Ea/RT)
k-rate constant
A-pre-exponential factor
e^(-Ea/RT)-The fraction of molecules with energy greater than the activation energy

Question 29

What is the rate determining step

Answer 29

The slowest step in the reaction mechanism. It governs the rate of the overall reaction

Question 30

A+B+C ---> Y + Z
1. A + B ---> (fast) D
2. D ---> (slow) E
3. E + C ---> Y + Z (fast)
What is the rate equation for this reaction

Answer 30

rate=[A][B][D]

2 is rate determining step but the rate of step 1 might effect the overall rate

Question 31

What is the iodine clock used to measure

Answer 31

The rate of reaction between hydrogen peroxide and potassium iodide

Question 32

How is the iodine clock measured

Answer 32

Adding a known number of sodium thiosulfate and starch which gives an end point when solution goes dark blue/black