OZ

Question 1

typical composition of troposphere

Answer 1

78% nitrogen gas
21% oxygen gas
1% argon gas
small amounts of methane, carbon dioxide, neon and helium

Question 2

mixing of gases vertically in troposphere and stratosphere

Answer 2

easy in troposphere - hot gases can rise and cold gases can fall
hard in stratosphere - reverse temperature gradient

Question 3

PPM =

Answer 3

% composition x 10000

Question 4

UV

Answer 4

most damaging part of electromagnetic spectrum to humans
absorbed by ozone in the stratosphere
UV B and UV C most damaging forms

high energy UV breaks down the molecules by breaking bonds and producing highly reactive radicals

Question 5

vibrational energy

Answer 5

supplied by IR radiation

Question 6

rotational energy

Answer 6

supplied by microwave radiation

Question 7

electronic energy

Answer 7

corresponds to energy provided by visible light and UV

Question 8

when an electron absorbs radiation:

Answer 8

electrons may be excited to higher energy levels
with higher energy photodissociation forming radicals may occur
with very high energy ionisation (removal of an electron) may occur

Question 9

homolytic fission

Answer 9

one of the two shared electrons goes to each atom (fission producing radicals)

Question 10

heterolytic fission

Answer 10

both of the shared electrons go to one of the bonding atoms, forming ions
atom which gains both the bonding electrons becomes negative ion

Question 11

radicals

Answer 11

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

Question 12

initiation

Answer 12

initial reaction in which a molecule produces radicals by photodissociation

Question 13

propagation

Answer 13

radicals react with another molecule and a new radical form

Question 14

termination

Answer 14

two radicals react and no radical is produced

Question 15

factors affecting rate of reaction

Answer 15

conc of solution/pressure of gas
surface area
intensity of radiation
temperature

Question 16

explaining the effect of concentration/pressure on rate

Answer 16

higher number of particles per volume
increased frequency of collisions
particles collide with sufficient energy
hence increases rate

Question 17

activation enthalpy Ea

Answer 17

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

Question 18

transition state

Answer 18

highest point on the pathway of a reaction where old bonds stretch and break, and new bonds begin to form

Question 19

breakdown of ozone by chlorine radicals

Answer 19

Cl + O3&raquo_space; ClO + O2
ClO + O&raquo_space; Cl + O2
overall : O + O3&raquo_space; 2(O2)

Question 20

importance of haloalkanes

Answer 20

used in fire retardants and as intermediates in medicine synthesis

Question 21

attraction of shared electrons in molecules

Answer 21

shared electrons are attracted more strongly by the core of the smaller atom, which is closer

shared electrons are attracted more strongly by the atom with the greater core charge

Question 22

electronegativity

Answer 22

measure of the tendency of an atom to attract a bonding pair of electrons
increases across a period and decreases down a group (increases towards fluorine)

Question 23

polar covalent bonds vs non-polar covalent bonds

Answer 23

polar occurs where there is a significant difference in electronegativity of the atoms involved

non-polar occurs with equal sharing of the bonding electrons or when there is only a small difference in electronegativity (diatomic molecules)

Question 24

trends in strength of intermolecular bonds (imbs)

Answer 24

bigger atoms/molecules have higher BPs because they form stronger imbs
longer chains have higher BPs because there are more points of contact for imbs
highly branched molecules have lower BPs because there are less points of contact for imbs

Question 25

dipole

Answer 25

molecule with a partially positive end and a partially negative end because of its polar bond

Question 26

permanent dipole

Answer 26

when two atoms have substantially different electronegativities

Question 27

induced dipole

Answer 27

occurs when an unpolarised molecule is next to a dipole (dipole attracts/repels electrons in the unpolarised molecule, inducing a dipole in it)

Question 28

instantaneous dipole

Answer 28

temporary dipole which arises when the electrons, which are constantly moving, in a molecule are unevenly distributed
all molecules have instantaneous dipoles
bigger molecules have more electons so produce more

Question 29

types of imbs from weakest to strongest

Answer 29

instantaneous dipole - induced dipole (in all molecules)
induced dipole - permanent dipole
permanent dipole - permanent dipole

Question 30

symmetrical molecules and dipoles

Answer 30

can have multiple bonds but no permanent dipole

negative charge is evenly spread across the molecule

Question 31

requirements for hydrogen bonds

Answer 31

large dipole between a H atom and a highly electronegative ion (O, N or F)
small H atom which can get very close to the electronegative atoms in nearby molecules
a lone pair on the electronegative atoms that the +ve H atoms can line up with

Question 32

MP and BP of fluorine

Answer 32

lower than the other halogens

has the weakest id-id bonds because it has the fewest electrons

Question 33

BP of hydrogen fluoride

Answer 33

appears to have unusually high BP compared to the other hydrogen halides
has the ability to form H bonds and the others do not
more energy required to break H bonds than id-id bonds

Question 34

nucleophile

Answer 34

molecule or -ve ion with a lone pair of electrons that it can donate to a +ve atom in order to form a covalent bond

Question 35

nucleophilic substitution of hydroxide ion and haloalkane

Answer 35

heat under reflux with NaOH and ethanol

OH- attacks the carbon atom in the C-X bond
OH- donates pair of electrons to form a new dative covalent bond
C-X bond breaks heterolytically, producing X- ion

Question 36

nucleophilic substitution of water and haloalkane

Answer 36

heat ender reflux (with water)

water molecule attacks carbon in C-X bond
lone pair on oxygen donated to form new dative covalent bond
C-X bond breaks heterolytically, producing X- ion
resulting molecules loses H+ to form an alcohol

Question 37

nucleophilic substitution of ammonia and haloalkane

Answer 37

heat in a sealed tube (with ammonia)

ammonia molecule attacks carbon in C-X bond
lone pair on nitrogen donated to form new dative covalent bond
C-X bond breaks heterolytically, producing X- ion
resulting molecules loses H+ to form an amine

Question 38

producing haloalkane from alcohol

Answer 38

halide ions are nucleophiles

requires presence of strong acid