OZ 4, 5

Question 1

define rate of reaction

Answer 1

the rate at which reactants are turned into products

Question 2

how to calculate the rate of reaction

Answer 2

rate of reaction + change in property / time taken

Question 3

how to calculate the rate of reaction between a group 2 carbonate and hydrochloric acid

Answer 3

it produces carbon dioxide
- react together in a conical flask with a bung and delivery tube inserted in it
- feed delivery tube into water in a trough with an upturned measuring cylinder with a clamp on it

Question 4

what are the different properties of a reaction you can pay attention to when measuring rate of reaction

Answer 4

• volume of gas evolved
• changes in mass
• pH measurement
• colorimetry
• chemical analysis

Question 5

how does chemical analysis work

Answer 5

• in interferes with the progress of the reaction
• take out a small sample of the reaction mixture and determine how much product or reactant is present

Question 6

which factors affect the rate of reaction

Answer 6

• concentration of reactants (mol/dm3)
• temperature
• intensity of radiation e.g. dissociation of oxygen molecules happens faster with more intense radiation
• particle size of a solid e.g. powder is much faster than a block
• the presence of a catalyst
• -

Question 7

what is collision theory

Answer 7

the idea that reactions occur when particles of reactants collide with a minimum amount of kinetic energy. This is more likely to happen if there are more molecules in a certain amount of space and each particle has a lot of energy.

Question 8

describe an enthalpy profile

Answer 8

• displays the energy changes that take place as a reaction proceeds
• the highest point on the graph corresponds to the transition state, which is where the old bonds stretch and the new bonds start to form

Question 9

what is the Maxell Boltzmann distribution

Answer 9

• the distribution of kinetic energies in a gas at a given temperature

Question 10

define activation enthalpy

Answer 10

minimum kinetic energy required by a pair of colliding particles before a reaction will occur

Question 11

how to catalysts work

Answer 11

they speed up the rate of reaction by providing an alternate reaction pathway with a lower activation enthalpy for bond breaking and the formation of new bonds

Question 12

how do catalysts affect:
- enthalpy change
- equilibrium

Answer 12

• the enthalpy change is the same for a catalysed and uncatalysed reaction
• they do not affect the equilibrium in a rate of reaction OR the rate at which the equilibrium is attained

Question 13

what is a homogeneous catalyst and how does it work

Answer 13

• it is when the catalyst is in the same physical state as the reactant
• they form an intermediate compound with the reactants (transition state)
• then the intermediate compound breaks down to form the products

Question 14

what happens to chloromethane and bromomethane in the stratosphere

Answer 14

• small amounts of each make it into the stratosphere
• the molecules are split up by solar radiation to give chlorine and bromine atoms
• these atoms then delete ozone

Question 15

write out the equations for chorine (or technically bromine) deleting ozone

Answer 15

Cl + O3 —-> ClO + O2
(ClO is another radical, which makes another radical when it reats with an oxygen atom)
ClO + O —-> Cl + O2
THEN
O + O3 —-> O2 + O2
Cl + O3 —-> ClO + O2

Question 16

why is the reaction of chlorine deleting ozone in stratosphere arguably significant

Answer 16

• both oxygen atoms and chlorine compete to delete ozone in the stratosphere
• but the concentrations of chlorine atoms is much smaller than oxygen atoms
• but when chlorine radicals delete ozone, the reaction happens 1500 X faster
• when chlorine atoms delete ozone, they generate ClO as a product, which reacts with more oxygen atoms to produce more Cl

Question 17

why are chlorine and bromine basically catalysts in the deletion of ozone
(and which is more effective)

Answer 17

they react with ozone the produce ClO and O2, then react with oxygen atoms to regenerate themselves in atomic form so they can go one and start the whole process again and delete more ozone

Question 18

what is the general equation for radicals deleting ozone ( use X )

Answer 18

X + O3 —> XO + O2
XO + O —> X + O2
—————————- (OVERALL)
O + O3 —-> O2 + O2

Question 19

what is the radical chain reaction for hydroxyl radicals deleting ozone

Answer 19

HO + O3 —-> HO2 + O2
HO2 + O —-> HO + O2