ozone story Flashcards
electronegativity definition
the ability for an atom to attract electrons towards itself in a covalent bond
electronegativity trend on periodic table
further up and further right you go, the more electronegative the element is (excluding group 8) i.e. fluorine is the most electronegative element
relationship between electronegativity and how ionic a compound is
the bigger the difference in electronegativity between molecules in a compound, the more ionic the compound will be
(a difference of zero will be purely covalent)
what are the intermolecular forces
- instantaneous dipole - induced dipole
- permanent dipole - permanent dipole
- hydrogen bonds
features of instantaneous dipole - induced dipole bond
- weakest type of imf
- exist between all atoms and molecules, even if non-polar
process of formation of instantaneous dipole - induced dipole bond
- random movement of electron creates a temporary instantaneous dipole
- instantaneous dipole produces an induced dipole in a neighbouring molecule
- id-id forces are the temporary attraction between an instantaneous dipole on one molecule and an induced dipole in a neighbouring molecule
trends in instantaneous dipole - induced dipole forces
- the strength of id-id forces increases with the polarisability of the molecule
- bigger atoms = more electrons = stronger id-id forces = higher bpt
- bigger molecule = more electrons = stronger id-id = higher bpt
- straighter chain molecule = more id-id opportunities = overall stronger id-id = higher bpt
permanent dipole - permanent dipole features
significantly stronger than id-id forces
permanent dipole - permanent dipole bond criteria
- must be polar (have electronegativity difference between atoms)
- must not be symmetrical
features of hydrogen bonds
strongest intermolecular force
hydrogen bond criteria
- O-H, F-H, or N-H bond in molecule
- H also bonding to O,N or F on other side
reasoning for hydrogen bond criteria
- O, N, F are the most electronegative elements so they can withdraw electrons, making H very partially positive
- H must bond to O, N, or F on other side because they have lone pair of electrons which are directly involved in H bond
- Hydrogen - because no inner electrons to shield nucleus when bonded to very electronegative element, the hydrogen nucleus is deshielded
hydrogen bonding in water
- not all possible hydrogen bond form
- molecules closer together
- more dense
hydrogen bonding in ice
- all 4 possible hydrogen bonds from to each water molecule
- this pushes water molecules slightly further apart
- open tetrahedral network
- ice is less dense than water
trends going from id-id, pd-id, pd-pd, to hydrogen bonding
- increase in strength of intermolecule force
- more energy needed to overcome force
- higher bpt, mpt, and viscosity
what is activation energy
Ea
the minimum energy required for a reaction to take place between two colliding reacting particles
what is an enthalpy profile
diagram showing enthalpy changes in a reaction
enthalpy profile for exothermic reaction
reactants higher than products
enthalpy profile for endothermic reaction
reactants lower than products
collision theory requirements for a reaction to occur
1 . successful collisions
2. energy > activation energy (achieved with temperature)
effect of concentration on rate of reaction
- increase in concentration = more molecules of substance in the same volume = more closely packed together = collisions between molecules become more likely and probability of a collision occurring with energy greater than or equal to activation energy increases
= rate of reaction increases
effect of pressure on rate of reaction
- increase in pressure has similar effect as increase in concentration as molecules are packed close together in a smaller volume
- rate of reaction increases
effect of increase in temperature on rate of reaction
- thermal energy transferred to substance
- converted to kinetic energy
- molecules of substance move faster + further = increased movement of molecules = collisions occur more often and with greater energy
- greater proportion of particles with an energy greater than the activation energy
- increased rate of reaction
effect of catalyst on rate of reaction
- catalyst lowers activation energy resulting in
- large increase in proportion of particles with energy greater than activation energy
- more frequent collisions with energy greater than activation energy
- increase in rate of reaction
role of catalysts
- increasing rate of reaction without being used up by providing an alternative reaction path with a lower activation energy
homogeneous catalyst meaning
catalysts that are in the same state as the reactants
working out the total volume of a mixture of gases
total volume of a mixture of gases = the sum of all the individual partial volumes in the mixture
converting between %volume and ppm
% – x10 to the power of 4 –> ppm
haloalkane functional groups
C - X
with X being a halogen
naming haloalkanes
X - alkane
e.g. bromoethane
2 - chlorobutane
amine functional group
- NH2
naming amines
(alkyl group) amine
e.g. methylamine
propylamine
haloalkane boiling points
induced dipole forces increase from F to I haloalkanes due to increased number of electrons
boiling point increases as the number of C atoms in chain increases
haloalkane reactivity series
increases going down the group
as bigger halogen, weaker bonds, easier to break, more reactive
haloalkane + water nucleophilic substitution reaction
haloalkane + water –> alcohol
haloalkane + water nucleophilic substitution reagents
water, ethanol cosolvent
haloalkane + water nucleophilic substitution conditions
heat to reflux
haloalkane + water nucleophilic substitution nucleophile
H2O:
haloalkane + alkali nucleophilic substitution reaction
haloalkane + NaOH –> alcohol
haloalkane + alkali nucleophilic substitution reagents
NaOH(aq), ethanol cosolvent
haloalkane + alkali nucleophilic substitution conditions
heat to reflux
haloalkane + alkali nucleophilic substitution nucleophile
:OH-
haloalkane + ammonia nucleophilic substitution reaction
haloalkane + ammonia –> amine
haloalkane + ammonia nucleophilic substitution reagent
concentrated NH3
haloalkane + ammonia nucleophilic substitution conditions
heat in a sealed tube, high pressure and temperature
haloalkane + ammonia nucleophilic substitution nucleophile
:NH3
nucleophile definition
an electron pair doner
substitution reaction definition
one functional group being replaced by a different functional group
why is iodoalkane more reactive than fluoroalkane
the C-I bond has a higher bond enthalpy than the C-F bond
heterolytic fission meaning
both electrons in bond move onto one atom
forms ions
more common in polar bonds + solvents
full curly arrow
homolytic fission meaning
one electron in bond moves onto each atom
forms radicals
more common in non-polar solvents and gas phase
two curly half arrows
radical definition
an atom or molecule with an unpaired electron
radical chain reaction process
- initiation (molecules -> radicals, homolytic fission)
- propagation (radicals -> radicals, pairs of steps)
- termination (radicals -> molecules)
what does a full headed arrow represent
two electrons moving
what does a half head arrow represent
one electron moving away
where do reactions of the ozone take place + why
reactions of ozone take place in the stratosphere, as in the stratosphere there is high energy u.v.
formation of ozone reaction
a) O = O –h.e u.v–> 2O radical (g)
b) O2 (g) + O (g) –> O3 (g)
depletion of ozone reaction
O3 (g) –h.e u.v –> O2(g) + O(g)
formation + depletion of ozone naturally
steady, rate of formation = rate of depletion, concentration of ozone remains constant
problem with ozone now
solar radiation causes haloalkanes that reach the stratosphere to split giving chlorine and bromine radicals
chloroalkane depletion of ozone propagation steps
a) Cl radical(g) + O3(g) -> ClO radical (g) + O2(g)
b) ClO radical (g) + O(g) -> Cl radical (g) + O2(g)
why do C-I molecules have no effect on ozone depletion
C-F bonds are the least likely to break, and C-I are the most likely
this is because C-F has the highest bond enthalpy and C-I the lowest
so most C-I bonds react before reaching the stratosphere, and thus have little effect on the ozone layer
uses of the ozone
absorbs most high energy UV radiation, preventing it from reaching surface (acts as a sunscreen)
effects of UV
- can break DNA and damage genes
- increases risk of skin cancer
- damages proteins in skin, making people look older
polluting effects of ozone in troposphere
- photochemical smog -> leads to irritation and respiratory problems
- ozone is tocis to humans
- UV radiation is one of the main ways humans produce vitamin D
radiation the sun emits, in order of increasing frequency
- infrared
- visible light
- ultraviolet
calculation to work out wavelength
wavelength (m) = speed of light / frequency (Hz)
calculation to work out the energy of a photon
energy of a photon (J) = planck’s constant x frequency (Hz)
calculation to work out bond enthalpy
bond enthalpy (kJmol-1) = energy of a photon (J) x avogadros constant
photodissociation process
- electrons in any molecule have fixed energy levels
- electrons may be excited to a higher energy level when they absorb radiation
- with even more energy, the bonding electrons will no longer be able to hold the bond and radicals will be formed (aka photodissociation)
- ionisation is also possible if there is enough energy for an electron to leave
what is the addition of energy from photons shortened to
+ hv
