The Ozone Story

Question 1

Converting from ppm to percentage

Answer 1

Divide by 1,000,000 and multiple by 100

Question 2

Energy of a photon = ?

Answer 2

Planck constant x Frequency

Question 3

What three things can happen when a molecule absorbs radiation

Answer 3

• Electrons can be excited to a higher energy state
• Photodissociation may occur and radicals are formed
• The molecules are ionised

Question 4

Heterolytic and homolytic fission

Answer 4

Heterolytic fission - both electrons go to the same atom in the bond

Homolytic fission - both atoms in the bond get one electron, this causes the formation of radicals

Question 5

Reactions for the breakdown of ozone

Answer 5

O + O2 –> O3
O + O –> O2
O + O3 –> O2 + O2

When added together:
O3 –> O2 + O

Question 6

The stages of a radical chain reaction

Answer 6

Initiation - the stage which creates the radicals, only radicals on the right

Propagation - the middles stages, radicals on both sides of the reactions

Termination - the final reaction, only radicals on the left

Question 7

Activation enthalpy

Answer 7

The minimum enery required by a pair of colliding particles before a reaction will occur

Question 8

Chlorine as a ozone depletion catalyst

Answer 8

Cl + O3 –> ClO + O2
ClO + O –> Cl + O2
——‐——‐—
O3 + O –> O2 + O2

Question 9

Hydroxyl radicals as a a ozone depletion catalyst

Answer 9

HO + O3 –> HO2 + O2
HO2 + O –> HO + O2
——‐——‐—
O3 + O –> HO + O2

Question 10

Nitrogen monoxide as a ozone depletion catalyst

Answer 10

NO + O3 –> NO2 + O2
NO2 + O –> NO + O2
——‐——‐—
O3 + O –> O2 + O2

Question 11

What is responsible for most of the properties and reactions of haloalkanes

Answer 11

The polar carbon-halogen bond, with the halogen being the negative side and the carbon being the positive side

Question 12

Electronegativity

Answer 12

A measure of the ability of an atom in a molecule to attract electrons in a chemical bond to itself

Question 13

How does the size of the molecule affect the intermolecular forces

Answer 13

A larger molecule has stronger intermolecular forces and therefore a higher boiling point

Straight-chain alkanes have higher boiling points than their branched isomers as the straight-chain provides more contact between molecules and more opportunity for intermolecular bonds to form

Question 14

What is a dipole and what are the types

Answer 14

A dipole is a molecule or part of a molecule with a positive end and a negative end, because of its polar bond

Permanent dipole-Permanent dipole
Permanent dipole-Induced dipole
Instantaneous dipole-Induced dipole

Question 15

Permanent dipole-Permanent dipole

Answer 15

Strongest form of intermolecular bond, formed between two molecules with permanent dipoles

Question 16

Permanent dipole-Induced dipole

Answer 16

The second strongest form of intermolecular bond. Occurs when a molecule with a permanent dipole induces a dipole in another molecule

Question 17

Instantaneous dipole-Induced dipole

Answer 17

A temporary dipole occurs in one molecule which then induces a dipole in another molecule. This is the weakest form of intermolecular bond

Question 18

Melting and boiling points of the halogens

Answer 18

Fluorine has the weakest intermolecular bonds as it is the smallest so melting and boiling points increase

Question 19

Hydrogen bonding

Answer 19

The strongest form of intermolecular bond and is a special case of permanent dipole-permanent dipole

For hydrogen bonding to happen:

• A large dipole between a hydrogen atom and a highly electronegative atom
• A small hydrogen bonding which can get close to the electronegative atom
• A lone pair of electrons on the electronegative atom

Question 20

Formation of radicals

Answer 20

A radicals are formed in the stratosphere when exposed to ultra violet light

Question 21

Nucleophile

Answer 21

A molecule or negatively charged ion with a lone pair of electrons that it can donate to a positively charged atom to form a covalent bond

Question 22

Which carbon-halogen bond will hydrolyse first and why

Answer 22

C-I bonds are most easily hydrolysed as they have the lowest bond enthalpy