The Ozone Story
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What does PPM stand for?
Parts per million Amount of gas particles in a sample containing 1 million particles
How can you calculate percentage composition from PPM?
ppm/1,000,000 x 100 = percentage composition AKA ÷ by 10,000 100% = 1,000,000ppm so 1% = 10,000ppm To convert from ppm to %, ÷ by 10,000
How can you calculate ppm from percentage composition?
% compostition/100 x 1,000,000 = ppm AKA x by 10,000 100% = 1,000,000ppm so 1% = 10,000ppm To convert from ppm to %, ÷ by 10,000
When might the concentration of gas in a mixture be given as percentage by volume?
When the gas is present in a high concentration e.g. various gases that make up the air in the atmosphere
When might the concentration of gas in a mixture be given in ppm?
If the gas is present in a low concentration - less than 1% by volume
Why is high energy UV radiation bad for the skin? What damage can it do?
Its wavelength/frequency corresponds to the energy required to break chemical bonds, such as DNA Therefore it can damage genes and lead to skin cancer or damage proteins and age the skin
What is the electromagnetic spectrum?
The range of wavelengths/frequencies over which electromagnetic radiation extends…
What is photodissociation?
Bond breaking caused by visible light/UV radiation
What do the surfaces of the Sun and Earth both emit?
EM radiation
What 2 equations link the 2 properties of light (i.e. wave-particle duality?)
c = λv E = hv Where λ = wavelength and v = frequency
How do you calculate the frequency needed to break a bond? AKA energy needed to cause photodissociation
Convert kJ/mol into J/mol by x1000 Work out the min. energy needed to break a single bond by ÷NA Divide energy by Planck’s constant (v = E ÷ h)
How do you calculate bond enthalpy from frequency?
Calculate energy needed to break 1 bond by using E = hv x NA to work out energy needed to break 1mol of bonds ÷1000 to give answer in kJ/mol
What are the 4 possible outcomes when molecules absorb EM raditation? Put them in order of decreasing energy (highest energy to lowest)
Electronic transmission between energy levels Vibration of bonds Rotation of whole molecule Translation of whole molecule (Electronic transmission = requires most energy)
Absorbtion of which types of EM radiation cause which outcomes (i.e. changes in molecule)? Match them up
Electronic transmission = Visible/UV Vibration = IR Rotation/Translation = Microwave
Why is the energy required to cause electronic transmission/vibration/rotation/translation given as a range despite the fact the outcomes are quantised?
The amount of energy needed to do each of these things changes depending on the chemical/substance
What 3 changes to a compound/substance can electronic transmission cause? Put them in order of decreasing energy requirement (i.e. from highest→lowest energy requirement)
Can cause: Ionisation - Cl2 → Cl2+ + e- Dissociation - Cl2 → Cl• + Cl• Release of energy + return to original state
How does the effect visible light/UV radiation have on matter differ?
Both cause electronic transmission… Vissible light causes electrons to be excited to higher energy levels and some bonds break UV causes electrons to be excited to higher energy levels and bonds break
What are the 2 ways covalent bonds can break? What are the products of each type of breaking?
Homolytic fission - produces ions Heterolytic fission - produces radicals
What is heterolytic fission?
Type of covalent bond breaking Both electrons from a shared pair go to same species Forms ions
What is homolytic fission?
Type of covalent bond breaking One electron from a shared pair goes to each species Forms radicals
What is a radical?
A species with one (or more) unpaired electron
What are curly arrows used to show? What are the 2 types and what do they denote?
Used to show the movement of electrons Full (double-headed) shows movement of a pair of electrons Half (single-headed) shows movement of a single electron
What is a radical chain reaction?
A reaction in which new radicals are formed at the end of one step These radicals then continue/propagate the reaction
What are biradicals? Give an example
Species with 2 unpaired electrons E.g. oxygen atoms Dots are not usually used