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Chem - A level (units 1 -10) > The Ozone story - Unit 4 > Flashcards

The Ozone story - Unit 4 Flashcards

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1
Q

What happens to the atmosphere the higher up you go?

A

It becomes less dense

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2
Q

What are the two most important parts of the atmosphere and there order?

A

1 - Troposphere

2 - Stratosphere

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3
Q

What does 339 ppm of N2 mean?

A

Out of one million particles in a sample of air, 336 will be N2 particles

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4
Q

How do you convert percentage to ppm?

A

x 10,000

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5
Q

What is the main source of anthropogenic CO2 emissions? (2)

A

1 - Combustion hydrocarbon fuels

2 - Deforestation

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6
Q

What is the main source of anthropogenic Methane emissions? (4)

A

1 - Cattle farming

2 - Landfill sites

3 - Rice paddy fields

4 - Natural gas leakage

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7
Q

What is the main source of anthropogenic Nitrous Oxide emissions?

A

1 - Fertalised soils

2 - Changes in land use (e.g from soil when land is ploughed)

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8
Q

What is the main source of anthropogenic Carbon Monoxide emissions?

A

1 - Incomplete combustion of hydrocarbosn - car exhausts

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9
Q

What is the main source of anthropogenic Nitrogen Oxides emissions?

A

1 - Internal combustion engines e.g from reaction of N2 and O2 at high temps

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10
Q

What is the most damaging type of electromagnetic radiation to the skin?

A

Ultraviolet

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11
Q

What is a positive effect of Ozone in the atmosphere?

A

1 - In the stratosphere, ozone absorbs high energy UV radiation

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12
Q

What are the damaging effects of UV radiation? (3)

A

1 - Damage DNA leading to skin cancer

2 - Damage eyes leading to cataracts

3 - Damge crops

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13
Q

What are the negative effects of Ozone in the atmopshere? (3)

A

1 - In the troposphere, is a pollutant

2 - Involved in reactions that produced photochemical smogs

3 - This causes: Reduced visability, respiratoty issues

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14
Q

Is the speed of light differnet for different elcrtomagntic raditaion?

A

No, it’s a constant

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15
Q

What is a key feature of electronic, rotational, translational and vibrational energy?

A

1 - All the types of energy are quantised, has a definite amount of energy

2 - This means they all occupy definite energy levels

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16
Q

What are the effects of infared radiation on your body? (2)

A

1 - Makes bonds in the chemicals in your skin vibrate more energetically

2 - The molecules have more kinetic energy resulting in you feeling warmer

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17
Q

What type of electromganetic radiation do, electronic, vibrational and rotational energy levels absrob?

A

Electronic - Visable + UV

Vibrational - Infared

Rotational - Microwave

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18
Q

Out of electronic, vibrational, rotational and translational energy changes, what requires the most energy and why?

A

1 - Electronic - Energy levels furthest apart

2 - Vibrational

3 - Rotational

4 - Translational

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19
Q

What are the three things that can happen when a Cl2 absorbs radiation?

A

1 - e- excited to higher energy level and energy released

2 - If higher energy photon absorbed - Photodissociation occurs - bonding e- can no longer bond the atoms together, forming a radical Cl

3 - If very high enery photon absorbed - Ionisatoion - e- is able to leav molecule

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20
Q

What are radicals?

A

1 - Molecules or atoms with atleast on unpaired e-

2 - Very reactive so can lead to further reactions

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21
Q

What’s another word for bond breaking?

A

Bond fission

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22
Q

What is heterolytic fission? (2)

A

1 - Both of the shared e- go to just one atom when the bond is broken

2 - This atom then becomes negativly charged because it has one more e- than proton and the other atom becomes positivley charged

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23
Q

What is homolytic fission?

A

The breaking of a covalent bond in which each bonding atom receives one electron from a bonding pair, forming two radicals

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24
Q

How are radicals most commonly formed?

A

When the bond being broken is non - polar

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25
Q

What conidtions increase the likliehood of a polar bond being broken by homolytic fission (2)

A

1 - Reaction taking place in the gas phase

2 - Presence of light

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26
Q

In homolytic fission, what can happen to the unpaired e- on the radicals? (2)

A

1 - The unpaired e- can be ommited and the radical represented as Br instead of Br.

5 - The unpaired e- has a strong tendency to pair up with another e- from another substance

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27
Q

How can Oxygen radical be formed?

A

The photodissociation of dioxygen molecules when UV radiation of the rigth frequencey is absorbed

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28
Q

What is a polar bond and when does it form? (2)

A

1 - Where one atom is slightly + and the other slightly -

2 - Happens when atoms have a different electronegativity

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29
Q

Why are radicals reactive?

A

They try to fill their outer shells by grabbing an e- from another atom or molecule

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30
Q

What does a full headed curly arrow represent?

A

The movemnet of a pair of e-

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31
Q

What does a half headed curly arrow represent?

A

The movemnet of a single e-

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32
Q

What is formed in the reaction between Methand and Chlorine?

A

1 - HCl

2 - Chloromethane

3 - Ethene

4 - Further substitution can form dichloromethane and trichloromenthane

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33
Q

What is a radical?

A

(molecules or atoms) with an unpaired electron

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34
Q

What is steady state?

A

Something is being made as fast as it’s being used up

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35
Q

How could you measure a colour change in a reaction?

A

Using a colorimeter

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36
Q

What is the equation for rate of reaction?

A

change in property

time taken

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37
Q

What is chemical analysis and what are it’s downfalls?

A

1 - Taking samples of the reaction mixture at intervals and quenching them (stopping the reaction int the sample). the samples are then analysed

2 - This interferes with the progress of the reaction

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38
Q

What factors affect the rate of reaction? (6)

A

1 - Catalyst

2 - Concentration of reactants

3 - Temp

4 - Pressure

5 - SA of reactants (particle size)

6 - Intensity of radiation

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39
Q

What is Activation enthalpy?

A

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

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40
Q

What is the transition state in an enthalpy profile?

A

The highest point on the pathway from reactants to products, where old bonds stretch and break and new bonds start to form

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41
Q

What is the effect of a temp rise of 10oc on rate reaction?

A

Doubles rate of reaction

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42
Q

What does the Boltzmann distribution curve show?

A

Distribution of molecular energies.

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43
Q

Why do reactions go faster at higher temperatures?

A

because a larger proption of the collding molecules have the minmum Ea needed to react

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44
Q

What is the relationship between Ea and the effect raising the temp has on a reaction?

A

The greater the Ea , the greater is the effect of increasing the temperture on the rate of reaction

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45
Q

Why do reactions go faster when using a catalyst? (2)

A

1 - Provide an alternative reaction pathway with a lower Ea

2 - Therefore, there is a larger proportion of particles that on collsion produce a sucessful collison

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46
Q

What does the dot represent B.?

A

The unpaired e-

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47
Q

What is an easy way of deciding whether or not something is a radical?

A

If then no. of e- shells is odd then it is a radical

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48
Q

What are the stages of a free radical chain reaction?

A

1 - Initiation

2 - Propogation

3 - Termination

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49
Q

What are the features of an initiation reaction? (3)

A

1 - One or more molecules react to form radicals

2 - A bond breaks by homolytic fission so the reaction is endothermic

3 - Often happens in the presence of uv light

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50
Q

What are the features of a propogation reaction? (3)

A

1 - A molecule and a radical react to form a new molecule / radical

2 - A bond breaks and a new bond forms

3 - Propagation reactions usually occur in pairs

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51
Q

What are the key features of a termination reaction? (2)

A

1 - Two radicals react to form one molecule

2 - A bond forms, so the step is exothermic

52
Q

Write an intitiation equation for Br2?

A

Br2 → Br● + Br●

53
Q

Write propgation equations for Br● + CH4, labelling the intermediate radical?

A

CH4 + Br● → CH3●(intermediate radical) + HBr

CH3● + Br2 → CH3Br + Br●

54
Q

Write an termination equation for two Br● radicals?

A

Br● + Br● →Br2

55
Q

How do you identify an intermdiate radical in a propgation reaction?

A

Add up the two reactions and the radical that appears on btoh sides are the intermediates

56
Q

What is CFC?

A

ChloroFlouroCarbon

57
Q

What are the features of CFC? (3)

A

1 - Very strong bonds

2 - These require a very high frequnecy radiation to break bonds

3 - Therefore, CFC very stable in troposphere

58
Q

Where can a CRC bond be broken and how? (2)

A

1 - Only in the stratopshere as has high enough frequency radiation

2 - A CRC bond then breaks by homolytic bond fission

59
Q

Why is NO deplete less O3 than CFC’s?

A

NO are water soluble wherease CFC’s are not, so NO’s absorb into atmopsheric moisture in the tropopshere so few reach the stratosphere

60
Q

How can a polar bond produce a non polar molecule?

A

If the e- are being pulled in equal but opposite directions

61
Q

What makes a molecule polar?

A

If the e- are being pulled in similar directions

62
Q

What is the strenght of the “id,id” effect?

A

Produces weak intermolecular froces between induced dipole and instantaneous dipole

63
Q

How does the Enthalpy change compare with a uncatalysed and catalysed reaction?

A

It is the same

64
Q

How do catalysts work in a reversable reaction?

A

They alter the rate at which the equilirium is obtained by not the composition of the equilibirum mixture

65
Q

What is a homogeneous catalyst and how do they work? (3)

A

1 - Catalyst in same physical state as reactants

2 - Form an intermediate compound with the reactants (transition state)

3 - The intermediate compound then breaks down to give the product and reform the catalyst

66
Q

Why does a Cl radical have a more significant effect on O3 depletion than O radicals?

A

1 - The reaction of Cl. + O3 is much faster than with the O<strong>.</strong>

2 - The Cl atoms are regnerated back into Cl. and go onto react wiht more O3

67
Q

Are Br radicals or Cl radicals more effective at destroying O3 ?

A

Br radicals

68
Q

Are all radicals highly reactive?

A

No, some are fairly stable

69
Q

Why does the enthalpy profile for the catlysed reaction have two humps? (3)

A

1 - Because an intermediate compound is formed with the reactant

2 - The intermediate is then broken down, giving a product and reforming the catalyst

3 - There is therefore two humps for the two steps

70
Q

What happens to the electronegativity of atoms as you go down a group and why?

A

1 - Electronegativity decreases

2 - The outer shell is further away from the nucleus, therefore the electrostatic attarction is less between the incoming e- and atom

71
Q

What happens to the electronegativity across a period?

A

Increases

72
Q

Where is the id-id effect present?

A

In all molecules

73
Q

What factors reduce the id-id forces?

A

1 - More branches

2 - Less e-

74
Q

What does pd-pd stand for?

A

permanent dipole - permanent diople

75
Q

What type intermolecular force is stronger , pd-pd or id-id and what does this mean? (3)

A

1 - pd-pd forces stronger than id-id forces

2 - Therefore more energy is required to overcome the force therefore a higher temp

3 - Therefore molecules with pd-pd forces have a higher bpt and mpt

76
Q

What is the key thing to rember about the interaction of pd-pd and id-id forces in molecules?

A

Even if a molecule has pd-pd forces it will always have id-id forces as well

77
Q

Put hydogrogen bonding, i-id effect and pd-pd effect in order of strength?

A

1 - Hydorgen bonding - strongest

2 - pd-pd - 2nd strongest

3 - id-id - weak

78
Q

Can you write id-id or pd-pd in exam?

A

NO

79
Q

What is a framework for explaining why a substance requires a higher temp to boil? (4)

A

1 - In X there are ‘instantaneous dipole - induced dipole’ and ‘permanent dipole- permanent dipole’ intermolecular forces between the molecules

2 - In Y there is also hydorgen bonding due to to the presence of the OH group

3 - Hydrogen bonds are stronger than ‘pd-pd’ interaction

4 - Therefore, Y has stronger intermolecular forces and requires more energy to overcome these forces and therefore requires a higher temp to boil

80
Q

Is CO2 polar?

A

No, is non poalar

81
Q

Between CO2 and SiO2, which one has the highest Bpt? (3)

A

1 - SiO2

2 - This is because it is a giant covalent structure and therefore contain strong covalent bonds which require lots of energy to break therefore a high temp is needed

3 - CO2 has weak id-id intermolecular forces which require little energy to overcome, therefore a lower temp is needed

82
Q

What is viscosity a measure of?

A

How strongly the molecules in the liquid attract each other

83
Q

When a liquid in a test tube is inverted, what must happen before a bubble can rise?

A

bonds between molecules must be broken as molecules are forced apart

84
Q

How do you decide which halogen prefix to put before the alkane?

A

Alphabetical order

85
Q

How is a small molecule of the same element held together? (2)

A

1 - Both nuclei are attracted to the shared e- between them

2 - Both atoms are identical so the e- are shared equally

86
Q

How are two atoms of different size or group bonded together and what does this cause ? (4)

A

1 - The smaller atom has a higher electronegativity as it’s nucleus is closer to the shared e-

or

2 - The nuclues with the greater charge has the highest e- so is closer to the e-

3 - This means this atom gets a slight neg charge beause it has a greater proprortion of the e-

4 - This forms a polar bond

87
Q

When a solid melts or boils what happens? (2)

A

1 - Intermolecular bonds are broken

2 - However any covalent bonds within the molecule remain intact

88
Q

What is the boiling point of nobel gases?

A

low

89
Q

What is the trend in Bpt of alkanes in relation to chain length? (3)

A

1 - The longer the chain

2 - The stronger the intermolecular forces

3 - The higher the Bpt

90
Q

What is the trend in Bpt of alkanes in relaton to braches? (2)

A

1 - In staright chain alkanes there is more contact between molecules and therefore more opportunities for intermolecular bonds to form

2 - Therefore straight chain alkanes have a higher Bpt than branched isomers

91
Q

What is a dipole?

A

A molecule with a pos end and a neg end

92
Q

What is said when a molecule has a dipole?

A

The molecule is polarised

93
Q

When do permanent dipoles occur?

A

When the two atoms in the bond have a substantial diff between electronegativities

94
Q

How is it possible for a molecule to not be polar but have polar bonds?

A

1 - The diples are moving in equal but opposite directions

2 - Therefore the dipoles cancel so there is no overall dipole - the molecule is non-polar

95
Q

How does an instantenaous dipole form? (3)

A

1 - In an instant, more of the - cloud is at one end of the molecule than the other

2 - The molecule therefore has an instantanoeus dipole

3 - The e- then change positions, changing the polarity of the molecule

96
Q

How does an induced dipole form? (2)

A

1 - When an instantaneous diploe/permanent dipole is next to the unpolarised molecule it can either attract or repel it’s e-

2 - This induces a dipole within the molecule

97
Q

What is the trend in Bpt of the halogens and why? (2)

A

1 - Going down the group the molecule are bigger and therefore have more e-

2 - Therefore the ‘id-id’ bonds increase and therefore the melting and Bpt increase

98
Q

How does HCl reduce the destruction of ozone? (2)

A

1 - It is a Chlorine reservoir molecule, therefore it stores Cl in the startosphere

2 - This therefore means less Cl is reacting with O3 and removing it

99
Q

What three features must the molecule involved have in order for hydrogen bonding to take place?

A

1 - H-N, H-F, H-O bonding to form a large dipole

2 - A small H+ to get very close to O,N or F atoms in the neighboring molecules

3 - A lone pair of e- on the O, N or F which the H+ can line up with

100
Q

Describe hydrogen bonding in HF? (4)

A

1 - The H atoms have a strong + charge because they are bonded to the highly electronegtive F atom

2 - The H+ lines up with the lone pair of e- on a neighboring F atom

3 - The H and F atoms get very close because the H atom is so small

4 - Therefore the H and F attract very strongly

101
Q

What effect does hydorgen bonding have on the viscosity of a substance? (4)

A

1 - Increases the viscosity because:

2 - When liquids flow the molecule move past eachother

3 - This requires the constant breaking and forming of intermolecular bonds

4 - Therefore, the stronger the bond the harder it is for the liquid to flow - increases viscosity

102
Q

What affect does hydrogen bonding have on the solubility of a substance?

A

1 - Makes it soluble in water

2 - This is because hydrogen bonds can form between water molecules and molecules of the substance, helping it dissolve

103
Q

Explain why water contains more hydrogen bonding than other substances (3)

A

1 - The O atom contains 2 lone pairs of e- and there are twice as many H atoms as O atoms

2 - This means there are as many hydrogen atoms as lone pairs

3 - Therefore the H+ can line up with the lone pairs, forming many hydrogen bonds

104
Q

Desrcibe the hydrogen bonding in ice?

A

There are 4 groups around each O atom therefore the hydrogen bonding between the molecules is maximised

105
Q

What is a nuclephile?

A

Something that can donate a pair of e- to form a covalent bond

106
Q

What feature must a nucleophile have?

A

1 - Must have a non-bonding pair of e-

107
Q

What are the reaction conditions needed for the reaction between NH3 nulceophile and a halogenolakane? (4)

A

1 - Conc. NH3

2 - aqueous

3 - Heat

4 - Sealed tube

108
Q

What are the conditions needed to make a halogenoalkane? (3)

A

1 - Hydrogen halide

2 - Conc. sulfuric acid + Na (halide)

or

  • Conc. phosphoric acid + Na (halide)

3 - Heat under reflux

109
Q

Why is ethanol added to the haloalkanes in the experiment ‘How do haloalkanes differ in reactivity’?

A

Haloalkanes are insoluble in water so the ethanol acts as a mutual solvent for the haloalkane, the water, and the silver ions so they mix together

110
Q

Breifly describe the experiment for ‘How do haloalkanes differ in reactivity?’ (3)

A

1 - React a know halogenoalkane with silver nitrate (aq) in the presence of ethanol and time how long it takes to go cloudy

2 - A lower time = More reactive

3 - Bond enthalpy matters more than bond polarity because the bond enthalpy differs more

111
Q

What are the points needed to include in the Exp. ‘How do haloalkanes differ in reactivity?’ (6)

A

1 - specified amounts

2 - How to measure e.g graduated pipette, burette

3 - 500c waterbath

4 - When to start timing and stop

5 - Why ethanol used

6 - Silver nitrate used as forms a precipiate with halide

112
Q

What are Substitution reactions involving water and hydroxide ions are known as?

A

Hydrolysis reactions

113
Q

What is a nucelophile?

A

A molecule or negativley charged ion with a lone pair of e- that it can donate to a poistivley charged atom to form a covalent bond

114
Q

What is substitution?

A

A reaction in which one atom or group in a molecule is replcaed by another atom or group

115
Q
A
116
Q

Describe the nucleophillic substituion reaction of 1-bromobutane and OH- ions? (4)

A

1 - The OH- nucleophile attacks the e- deficient carbon atom in the C-Br bond

2 - The OH- ion then donates 2e- to from a new dative covalent bond with the carbon atom

3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.

4 - The Bromine ion is the leaving group

117
Q

What does heating under reflux mean?

A

Heating without loss by evaporation

118
Q

Describe the hydrolyis reaction of 1-bromobutane? (4)

A

1 - The lone pair of e- on the O atom in the water nucleophile attacks the e- deficient carbon atom in the C-Br bond

2 - The water then donates 2e- to from a new dative covalent bond with the carbon atom

3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.

4 - The resulitng ion then loses H+ to form an alchohol and HBr

119
Q

Describe the nucleophillic substituion of Bromobutane and Ammonia? (4)

A

1 - The lone pair of e- on the nitrogen atom in the ammonia nucleophile attacks the e- deficient carbon atom in the C-Br bond

2 - The ammonia then donates 2e- to from a new dative covalent bond with the carbon atom

3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.

4 - The resulitng ion then loses H+ to form an amine and Hbr

120
Q

What is the general formula for amines?

A

R-NH2

121
Q

Describe the production of a haloalkane from an alchohol? (5)

A

1 - In the presence of a strong acid:

2 - The Oxygen atom donates a pair of e- to the H+ ion to form a dative covalent bond

3 - This gives the Oxygen atom an overall positive charge

4 - This gives the Carbon atom attached to the Oxygen a higher partial positive charge so it is now more readily attacked by halide ions

5 - Haloaklane + water then formed

122
Q

What would you expect a poalar bond to do?

A

The bond would be hydrolysed easier

123
Q

Watsthe reactivity of fluro compounds?

A

Unreactive as the C-F bond enthalpy is too high

124
Q

What was the response to Ozone depletion?

A

1 - Restricting the release of CFC’s and ozone depleting subatnces into the atomsphere

2 - Finding replcaments for CFC’s e.g HCFC’s as the H-C bonds mean the HCFC’s are broken down in tropsphere

  • However, some HCFC’s do make it to stratopshere where they photodissociate to produce Cl radicals - but still have no O3 depleting effect
125
Q

What effect does a catalyst have on equillibrium?

A

No effect

Chem - A level (units 1 -10) (14 decks)

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