The Ozone Story

Question 1

what is homolytic fission?

Answer 1

one electron goes to each atom, forms radicals

Question 2

what is heterolytic fission?

Answer 2

both electrons are transferred to one atom, forms a cation and an anion

Question 3

what is a substitution reaction?

Answer 3

when a functional group in a compound is replaced by another functional group

Question 4

what is a nucleophile?

Answer 4

an electron pair donor

Question 5

what reagents and conditions are required for nucleophilic substitution of a haloalkane?

Answer 5

-warm aqueous NaOH heated under reflux

Question 6

what reagents and conditions are required for nucleophilic substitution of haloalkanes with ammonia?

Answer 6

-warm a haloalkane with xs of ethanolic ammonia

Question 7

what determines reactivity of a haloalkane?

Answer 7

-bond strength (decreases down group)

Question 8

what happens in an initiation reaction?

Answer 8

• photodissociation causes bond to split homolytically

- 2 uncharged radicals produced

Question 9

How is Ozone made from Oxygen?

Answer 9

• O2 molecule absorbs UV, causing it to split into O radicals
• radicals combine with O2 to give O3

Question 10

what is a radical?

Answer 10

-a molecule with one unpaired electron

Question 11

How is ozone made in the troposphere?

Answer 11

-effect of sunlight on mixtures of Nitrogen Dioxide and hydrocarbons

Question 12

what are sources of atmospheric hydrocarbons and NO2?

Answer 12

• vehicle engines

- power stations

Question 13

what is photochemical smog and why is it dangerous?

Answer 13

• ozone mixed with solid particles of carbon and other substances
• causes respiratory problems

Question 14

what are CFCs?

Answer 14

haloalkanes that have all their hydrogen atoms replaced by chlorine and fluorine

Question 15

where does the breakdown of CFCs occur?

Answer 15

in the stratosphere

Question 16

how does the breakdown of CFCs result in destruction of the ozone layer?

Answer 16

• CFCs broken down by high energy UV, produce radicals
• Cl radicals are catalysts + react w/ Ozone to make ClO and O
• overall reaction is 2O3 -> 3O2

Question 17

what is the percentage of Nitrogen and Oxygen in the Atmosphere?

Answer 17

N2 =78%

O2 =21%

Question 18

define ‘dipole’

Answer 18

a difference in charge between the two atoms caused by a shift in electron density

Question 19

what is electronegativity?

Answer 19

the ability of an atom to attract the bonding electrons in a covalent bond

Question 20

why might a molecule containing multiple polar bonds have no overall dipole?

Answer 20

polar bonds are pointed in opposite directions, they cancel out

Question 21

explain how instantaneous dipole-induced dipole bonds arise?

Answer 21

• electrons in charge clouds constantly moving, this means that a temporary dipole can arise
• this dipole can induce another, temporary dipole in another molecule

Question 22

why do heavier molecules form stronger intermolecular bonds?

Answer 22

-larger molecules have larger electron clouds

Question 23

why do longer chained alkanes have higher boiling points than more branched isomers?

Answer 23

-more molecular surface contact means that there are more electrons that can interact

Question 24

why is ice less dense than water?

Answer 24

• in ice, the molecules are arranged so that there is the maximum amount of Hydrogen bonds, this ‘wastes’ space
• when the ice melts, bonds can form closer together

Question 25

explain how an increase in temperature increases rate of reaction

Answer 25

• higher number of molecules with activation enthalpy

- frequency of successful collisions increases