OZ 1, 2, 3

Question 1

what are the names of the parts of the atmosphere from top to bottom?

Answer 1

-thermosphere
-mesosphere
-stratosphere
-troposphere

Question 2

how do the sections of atmosphere vary in density and temperature

Answer 2

• the higher up that you go, the less dense it becomes (90% of all molecules are found in the troposphere)
• the higher that you go, the hotter it becomes, because hot gases rise and cold gases fall

Question 3

what is gas measured in when the concentration is small

Answer 3

parts per million (ppm)

Question 4

describe and explain the evolution of the atmosphere `

Answer 4

• there was originally very little oxygen, and the first simple plants began producing oxygen by photosynthesis
• when o2 conc reached about 10%, animals began to evolve by respiration
• the oxygen conc remained at 21%
• human activities add more gases to the atmosphere e.g. CFCs and HFCs and increase the conc of others e.g. carbon dioxide

Question 5

what are the effects of electromagnetic radiation

Answer 5

-breaks bonds in DNA molecules, causes damage to genes and can lead to skin cancer
-causes damage in proteins in the skin, years of exposure causes one to look wrinkly
-irritates blood vessels which causes skin to look red and burn

Question 6

why can you get sun burnt under water but not when sitting in a green house

Answer 6

the glass of the green house absorbs the ultra violet radiation but water does not absorb all of it

Question 7

what do sunscreens contain and why

Answer 7

contain many benzene rings or alternating double and single bonds so when uv light is absorbed, electrons in pi bonds jump to higher energy levels

Question 8

where is most uv light absorbed

Answer 8

upper atmosphere called the stratosphere

Question 9

what absorbs most uv light

Answer 9

ozone, oxygen gas in the form of O3

Question 10

where is ozone a pollutant and why

Answer 10

at ground level in the troposphere because it’s involved in reactions that produce photochemical smog

Question 11

what is the speed of light

Answer 11

3.00 X 10^8 m/s

Question 12

equation for the speed of light

Answer 12

c = wavelength (m) X frequency (s)

Question 13

how to calculate the energy of a photon

Answer 13

E (J) = planks constant (Js) X frequency (s)

Question 14

what is planks constant

Answer 14

6.63 X 10^-34 Js

Question 15

what are the different kind of electron activities in order of increasing energy

Answer 15

• translation
• rotation
• vibration of the bonds
• electronic energy
  these all involve different amounts of energy

Question 16

define electronic energy being quantised

Answer 16

it has fixed levels

Question 17

what causes molecules to vibrate

Answer 17

infrared radiation
spacing between vibrational energy levels corresponds to the infrared part of the spectrum.
makes bonds in skin chemicals vibrate more energetically, they gain kinetic energy which is why we sense it as heat

Question 18

what causes molecules to rotate

Answer 18

• requires less energy than vibrational, therefore corresponds to a lower energy part of the EM spectrum
• the microwave region

Question 18

what causes changes in electronic energy

Answer 18

• higher than all levels
• exciting electrons to a higher electronic energy level requires energy corresponding to visible and UV parts of the spectrum

Question 19

what three things can happen when a molecule absorbs radiation

Answer 19

1. electrons can be excited to a higher energy level
2. if the radiation is higher energy, the bonding electrons can no longer hold the atoms together (photodissociation)
3. if the photon is very high energy, the electron can leave the molecule so it is ionised

Question 20

define radical

Answer 20

molecules or atoms with at least one unpaired electron, and are usually very reactive

Question 21

what is heterolytic fission

Answer 21

both of the shared electrons go to the same atom, and it then becomes negatively charged

Question 22

what is homolytic fission

Answer 22

the two shared electrons each go to different atoms, they are each written with a dot beside them

Question 23

how is ozone formed

Answer 23

when an oxygen atom reacts with a dioxygen molecule

Question 24

how is ozone formed in the troposphere

Answer 24

by the action of sunlight on the pollutant of nitrogen oxide

Question 25

hoe is ozone formed in the stratosphere

Answer 25

photodissociation of dioxygen molecules when uv radiation of the right frequency is absorbed
(10.1 - 14) X 10^14

Question 26

why are radicals really reactive

Answer 26

they’re always trying to grab electrons from other atoms or molecules

Question 27

name and escribe the stages of a radical chain reaction

Answer 27

initiation - starts with no radical, ends with a radical
propagation - starts with a radical and ends with a different one
termination - starts with a radical, doesn’t end with one

Question 28

write out radical chain reaction of hydrogen chloride formation

Answer 28

INITIATION
Cl2 + hv —–> Cl* + Cl*
PROPAGATION
Cl* + H2 —-> HCl + H*
H* + Cl2 —-> HCl + Cl*
TERMINATION
H* + H* —-> H2
Cl* + Cl* —-> Cl2
H* + Cl* —-> HCl

Question 29

what is the radical chain reaction for methane and chlorine

Answer 29

initiation
Cl2 + hv —-> Cl* + Cl*
propagation
Cl* + CH4 —-> HCl + CH3*
CH3 + Cl2 —-> CH4 + Cl*
termination
CH3* + Cl* —-> CH3Cl
Cl* + Cl* —-> Cl2
CH3* + CH3* —-> C2H6