The Ozone Story Flashcards
Converting from ppm to percentage
Divide by 1,000,000 and multiple by 100
Energy of a photon = ?
Planck constant x Frequency
What three things can happen when a molecule absorbs radiation
- Electrons can be excited to a higher energy state
- Photodissociation may occur and radicals are formed
- The molecules are ionised
Heterolytic and homolytic fission
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
Reactions for the breakdown of ozone
O + O2 –> O3
O + O –> O2
O + O3 –> O2 + O2
When added together:
O3 –> O2 + O
The stages of a radical chain reaction
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
Activation enthalpy
The minimum enery required by a pair of colliding particles before a reaction will occur
Chlorine as a ozone depletion catalyst
Cl + O3 –> ClO + O2
ClO + O –> Cl + O2
——‐——‐—
O3 + O –> O2 + O2
Hydroxyl radicals as a a ozone depletion catalyst
HO + O3 –> HO2 + O2
HO2 + O –> HO + O2
——‐——‐—
O3 + O –> HO + O2
Nitrogen monoxide as a ozone depletion catalyst
NO + O3 –> NO2 + O2
NO2 + O –> NO + O2
——‐——‐—
O3 + O –> O2 + O2
What is responsible for most of the properties and reactions of haloalkanes
The polar carbon-halogen bond, with the halogen being the negative side and the carbon being the positive side
Electronegativity
A measure of the ability of an atom in a molecule to attract electrons in a chemical bond to itself
How does the size of the molecule affect the intermolecular forces
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
What is a dipole and what are the types
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
Permanent dipole-Permanent dipole
Strongest form of intermolecular bond, formed between two molecules with permanent dipoles
Permanent dipole-Induced dipole
The second strongest form of intermolecular bond. Occurs when a molecule with a permanent dipole induces a dipole in another molecule
Instantaneous dipole-Induced dipole
A temporary dipole occurs in one molecule which then induces a dipole in another molecule. This is the weakest form of intermolecular bond
Melting and boiling points of the halogens
Fluorine has the weakest intermolecular bonds as it is the smallest so melting and boiling points increase
Hydrogen bonding
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
Formation of radicals
A radicals are formed in the stratosphere when exposed to ultra violet light
Nucleophile
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
Which carbon-halogen bond will hydrolyse first and why
C-I bonds are most easily hydrolysed as they have the lowest bond enthalpy
