THE OZONE STORY

Formula for ozone

O3

What does UV do to bonds?

Causes bond breaking, homolytic fission to make radicals (photodissociation)

What does visible light do?

Causes electrons transitions between energy levels (emission spectroscopy)

What does IR do to bonds?

Causes bonds to vibrate more

What does microwave do?

Causes molecules to rotate

What is the percentage of nitrogen in the atmosphere?

78%

What is the percentage of oxygen in the atmosphere?

21%

What is the percentage of argon in the atmosphere?

1%

What is the ppm of CO2 in the atmosphere?

~400ppm

Where is the ozone layer located in?

The stratosphere

Between the stratosphere and the troposphere, which is the closest to the earth surface?

Troposphere

Ozone in the troposphere is…

Bad, respiratory irritant

Ozone in stratosphere is…

Good, absorbs high frequency UV from the sun which would otherwise cause skin cancer, eye damage and crop damage

How do you convert % to ppm?

x 10000

How do you convert ppm to %?

Divide by 10000

What is the shape and bond angle of ozone?

Non-linear / bent, 117.5°

State the type of bonding and structure of ozone

Simple covalent

What are the 2 reactions / equations to FORM O3?

O2 —> 2 O•

O2 + O• —> O3

Is the reaction ‘O2 —> 2 O•’ endothermic or exothermic? and explain why.

Endothermic, bc only breaking bonds

Is the reaction ‘O2 + O• —> O3’ endothermic or exothermic? and explain why.

Exothermic, bc only forming bonds

What’s the state of ozone at RTP?

Gas

How would you convert Kjmol^-1 to J?

x 1000 and divide by avogadros constant

(Exam question) State and explain shape and bond angle of ozone

There are 2 bonding groups of electrons and 1 LP around the central atom which repel to ger as far apart as possible, LP repel more than BP so decreases the bond angle by 2.5. 117.5, non-linear.

Equation linking energy and frequency:

E = hv

What is v in E=hv ? And give the units

Frequency / Hz

What is E in E=hv ? And give the units

Energy / J

Equation linking frequency and wavelength (in words):

Wavelength = speed of light / frequency

Converting nm to m

X10^-9

What are the 2 reactions of the breakdown of O3?

O3 —> O2 + O•

O3 + O• —> 2 O2

What is required for the reaction O3 —> O2 + O• to occur?

UV

How do you convert Kj to Kjmol^-1 ?

x 6.02 ×10 ^23

What is the value of the Avogadro’s constant

6.02 × 10²³

What is a catalyst?

A substance which increase rate of reaction by providing an alternative pathway with a lower Ea

What can catalyse the destruction of ozone?

Chemical species called radicals

What the name of a substance that is made in a step and then used in another?

Intermediate

What is a radical?

A radical is a species with an unpaired electron

Step 1 general pattern equation for the catalysed destruction of ozone

X• + O3 —> XO• + O2

Step 2 general pattern equation for the catalysed destruction of ozone

XO• + O —> O2 + X•

How is radicals formed?

When bonds are broken by UV (photodissociation)

What is photodissociation?

When bonds are broken by UV

What type of bond breaking forms radicals?

Homolytic fission

How do bonds break in heterolytic fission?

Due to kinetic energy / collisions with other molecules

How do bonds break in homolytic fission?

Due to UV

What are the 3 stages of radical reactions?

Initiation, propagation and termination

Define an initiation reaction

When radicals are made (from non-radical)

Define an propagation reaction

When one radical is used and another is made

Define an termination reaction

2 radicals react together to form a non-radical

Which type of energy breaks bonds during heterolytic fission

Kinetic energy

What is an example of a (organic) radical reaction?

Radical substitution of alkane

What is the standard (word) equation for a radical substitution of alkanes?

Alkane + halogen (UV) —> haloalkane + hydrogen halide

Why is it the Cl-Cl bond that breaks and not C-H or C-C?

Because Cl-Cl bond is the weakest

Why are radical reactions sometimes called chain reactions?

Because of the propagation steps

Why don’t industrial chemists use radical reactions often?

A mixture of products are made / cannot control reaction

What radical is NEVER made during radical substitution of alkane?

H•

What is a haloalkane?

Alkanes with one or more halogen atoms

Solubility of haloalkanes

Immiscible in water, cant make H-bonds with water

What type of molecules are haloalkanes?

Simple covalent

Bpt / mpt of haloalkanes

Fairly low due to weak intermolecular forces

State of haloalkanes at RTP

Mainly liquids

What reaction is used to make haloalkanes using an alkane?

Radical substitution of alkAne using a halogen

What is the type of reaction and the 2 types of reactants that can make haloalkanes from an alkene?

Electrophilic addition with halogen / with hydrogen halide

What does ‘nucleophilic’ mean in nucleophilic substitution?

Attacked by nucleophiles

What is a nucleophile?

A species that is negative or partially negative and can form a dative bond by donating a lone pair of electrons

In a reaction, between OH- and H2O, which would give the fastest reaction and why?

OH- reacts faster / is a better nucleophile than H2O / has a full negative charge

What haloalkane reacts the fastest? and why?

Iodoalkane reacts fastest as C-I is weaken than C-Br / C-Cl

What is electronegativity?

Is the ability of an atom to attract bonding electrons

Why would -CN not be a suitable nucleophile?

It is toxic

Why would NaOH not be a suitable nucleophile?

Its alkali / corrosive

Haloalkanes are immiscible. What solvent is added to allow haloalkanes to mix with water?

Ethanol

All equation must show conservation of ______ and conservation of ______.

Atoms / charge

What are the 4 elements with the highest electronegativity?

F / O / N / Cl

What does electronegativity depend on?

Size of atom / amount of protons

What is the definition of electronegativity?

The ability of an atom to attract bonding electrons

Which element has the highest electronegativity?

Fluorine

What would happen (in terms of e-) if two atoms bond with the same electronegativity?

They will have equal share of the electrons

(Just copy this) If 2 atoms bond with different electronegativities bond they will have an unequal share of the electrons → uneven distribution of charge → a polar bond

If 2 atoms bond with different electronegativities bond they will have an unequal share of the electrons → uneven distribution of charge → a polar bond

Electronegativity is a property of _______.

Atoms

What is the order from strongest to weakest of IMF?

Hydrogen bonding / PD-PD / ID-ID’s

What is activation energy?

The minimum combined energy 2 particles must have to react when they collide

Convert 1% to ppm

10000ppm

Are the strengths of (individual) H-bonds different or the same?

Same strength

How would the overall bpt/mpt due to H-bonds differ?

Higher number of H-bonds = higher mpt/bpt

What is viscosity?

The resistance of a fluid to a change in shape or movement

How does the strength of PD-PD’s differ?

They are all the same strength

How are ID-ID’s formed?

The random movement of electrons creates an instantaneous dipole, which induces a dipole in neighbouring molecules

What is an instantaneous dipole?

A temporary uneven distribution of charge

What directions do ID-ID’s cause attraction?

All directions

How does the strength of ID-ID’s differ?

Mr / shape of molecule

How does the shape of molecules increase the strength of ID-ID’s ?

More linear shape = packed more closely together = stronger ID-ID’s

How does the Mr of an atom increase the strength of ID-ID’s

Higher Mr = more e- = more polar = stronger ID-ID’s

Explain why fluorine is a gas at room temperature but iodine is a solid? [3]

Both have IDID’s / F2 has weaker IDID’s as it has lower Mr / Less E to break IDID’s for F2 so the bpt is below RT

What has to happen for a reaction to occur?

Particles must collide with E> the Ea / with the correct orientation

Why are reactions fastest at the start? (initial rate)

There is the highest probability of collisions between reactants

What is the definition of rate?

Change in the concentration of reactants or products over time

State all the factors that can alter the rate of a reaction?

Concentration / pressure / surface area / temperature / catalyst

What is the y-axis of a maxwell boltzmann distribution graph?

Number of collisions or particles

What is the x-axis of a maxwell boltzmann distribution graph?

KE