OCR Chemistry Salters ATMOSPHERE

Whole set of notes from Chemical Ideas on the Atmosphere Module. Enjoy, hope they help!

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Charlotte Jones Atmosphere Module Notes 18/04/13
Atmosphere ­ Notes for Chemistry Salters B
6.2 ­ What happens when radiation interacts with matter?
INTRO
Changes to molecules depend on:
o Molecule involved
o The amount of energy involved.
Changes can include:
o TRANSLATION ­ molecule moving around
o ROTATION ­ molecule rotating
o VIBRATION ­ of molecule bonds
o ELECTRONS ­ changes to electrons can occur
Stages occur as shown below (taken from Chemical Ideas textbook)
ELECTRONIC ENERGY
o Electronic energy is QUANTITISED at fixed levels.
o The more energy absorbed, the more the molecule rotates/vibrates etc as it moves
to a higher energy level.
o Different frequencies of energy causes different effects:
INFRARED ­ causes vibration
MICROWAVE ­ causes rotation
VISIBLE and UV ­ cause change of electronic level (electrons move to higher
levels)
o The TYPE OF BOND involved has an effect:
Stronger bonds require more energy to move to different energy levels.
CHANGES WHEN A MOLECULE ABSORBS UV RADIATION
o Electrons are excited to higher energy levels. When they fall back down to ground
state, they are UNCHANGED.
o If a higher energy is used, bonding electrons can no longer bond the atoms together
so the molecule breaks apart. This is called PHOTODISSOCIATION.
o RADICALS (free, unpaired electron) are formed as a result of PHOTODISSOCIATION.
o With very high energy, the electrons may leave the molecule, therefore it is IONISED.

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Charlotte Jones Atmosphere Module Notes 18/04/13
6.3 ­ Radiation and Radicals
WAYS OF BREAKING BONDS (BOND FISSION)
o HETEROLYTIC fission
Both of the shared electrons go to one of the atoms.
Leaves a +ve and a ­ve atom
Most common when a bond is POLAR
o HOMOLYTIC fission
Electrons are equally shared between the atoms.
Produces radicals (highly reactive)
RADICALS
o A molecule with an unpaired electron. (Odd number of electrons)
o BIRADICALS can be formed if a molecule has two unpaired electrons.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
10.1 ­ Factors affecting reaction rates
FACTORS AFFECTING RATE
CONCENTRATION
o The higher the concentration the faster the rate of reaction as there's a
greater chance of reactants colliding and more collisions take place.
TEMPERATURE
o The higher the temperature, the faster the rate of reaction as molecules have
more energy, so move faster thus increasing the chance and number of
collisions.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
10.2 ­ The effect of temperature on rate
RAISING THE TEMPERATURE
o Molecules move faster, so they collide more frequently.
o Average speed of molecules is proportional to
o Molecules collide with more energy, so activation energy is reached easier.
GRAPHS TO SHOW HOW TEMPERATURE AFFECTS RATE
This graph shows that there are a greater proportion of molecules with a higher kinetic
energy at 310K than 300K.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
10.5 ­ What is a catalyst?
TYPES OF CATALYSTS
o HETEROGENEOUS
Heterogeneous catalysts are in a DIFFERENT PHASE to the
reactants. (Different state)
The reaction (if solid catalyst and gaseous reactants) will
take place on the surface of the catalyst.
The process is shown on the right.
Reactants are adsorbed onto the surface of the
catalyst.
The bonds are weakened and
broken.
New bonds are formed and the
product diffuses away from the
catalyst surface.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
o Existing bonds are stretched and broken.
o New bonds are formed.
o BOND BREAKING is ENDOTHERMIC (it uses energy)
o BOND MAKING is EXOTHERMIC (releases energy)
o Catalysts speed up reactions by providing an alternative reaction pathway.
o This allows more molecules to react as the activation energy is lower.
o This graph shows that the activation enthalpy for the catalysed reaction is
smaller
that the
activation energy for an uncatalysed reaction.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
POSITION OF EQUILIBIRUM
o The position of the equilibrium depends on various factors
CONCENTRATION of solutions
PRESSURE of gases
TEMPERATURE
CONCENTRATION
o If the reactant concentration on one side of the reaction is increased, more
products will be made to counteract it.
Increasing the concentration of reactants causes the equilibrium to
move to the product side.…read more

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Charlotte Jones Atmosphere Module Notes 18/04/13
o SO2 has STRONG intermolecular bonds as it forms COVALENT BONDS
between molecules, making it hard to break apart. Thus it is a SOLID at room
temperature.
COVALENT MOLECULAR STRUCTURES ­ eg. CO2
o Consist of DISCRETE MOLECULES
o Strong covalent bonds between atoms
o DISSOLVE in organic solvents
COVALENT NETWORK STRUCTURE ­ eg. SO2
o Consist of giant repeating LATTICES of COVALENTLY BONDED atoms.…read more

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john k

Thanks for this, it's a great resource. 

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