The Atmosphere F332 Salters B

Revision notes covering the Atmopshere topic as part of F332, Salters B

HideShow resource information
  • Created by: H
  • Created on: 12-04-13 14:38
Preview of The Atmosphere F332 Salters B

First 506 words of the document:

The Atmosphere
Chlorofluorocarbons (CFCs)
CFCs are used are refrigerants, propellants in aerosols, blowing agents for making expanded plastics
and as cleaning solvents. CFCs are good for this because of their low reactivates, low boiling points,
low toxicity and high stability.
However, CFCs are estimated to have a lifetime in the troposphere of around 100 years. When they
reach the stratosphere they undergo photo dissociation to produce chemical radicals which then go
on to remove ozone.
In the early 1970s Sherry Rowland and Mario Molina predicted that CFCs would damage the ozone
layer. They were proved correct in 1985 when a team, led by Joe Farman, identified a hole in the
ozone over the Antarctic using ultraviolet spectroscopy. The computers for NASA satellites had
treated very low ozone reading as anomalies. Conclusive proof that CFFs were responsible for ozone
depletion was obtained when an aircraft flew through the stratosphere over Antarctica and measure
the concentrations of ClO and O3. The rapid fall in O3 occurred at exactly the point where ClO
concentrations rose. The link had finally been made. Findings from many parts of the scientific
community had succeeded in validating the results of all the work.
Alternatives to CFCs
Replacements have been used for CFCs although they in turn have their own problems.
Replacement Advantages Disadvantages
Hydrochlorofluorocarbons H-C bonds are broken down in Are greenhouse gases that
(HCFCs) and the troposphere before the contribute to global warming
hydrofluorocarbons (HFCs) compounds have a chance to
reach the stratosphere
Alkanes Alkanes don't contain chlorine Are flammable and greenhouse
The Greenhouse effect
The Greenhouse effect keeps the troposphere at a temperature that enables life to exist on earth.
High energy radiation from the Sun (mostly visible and UV radiation) reaches the Earth's surface and
some frequencies are absorbed. The Earth's surface is warmed and re-emits lower energy infrared
radiation. Greenhouse gases such as CH4 and CO2 absorb some of this radiation- the rest escapes
into space. A steady state is reached where the Earth radiates and absorbs radiation at the same
rate. The absorption of infrared radiation by greenhouse gases can cause atmospheric warming in
two ways:
Some infrared radiation is re-emitted by the molecules in all directions ­ some energy is
radiated back towards Earth and some out into space.
Absorption of infrared radiation increases the vibrational energy of the molecules ­ their
bonds vibrate more vigorously. Energy is transferred to other molecules in the atmosphere
by collisions. This increases their kinetic energy and raises the average temperature of the
Carbon dioxide and water are important greenhouse gases. CO2 and H2O absorb in two bands
across the Earth's radiation spectrum. Between these two bands is a `window' where infrared
radiation can escape without being absorbed. About 70% escapes through this fixed range of

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Is human activity responsible?
Human activities are increasing the atmospheric concentrations of `natural' greenhouse gases
e.g. CO2 and gases that are not naturally present e.g. CFCs. Although only present in small
amounts, each CFC molecule has a large `global warming potential' (GWP).
These gases absorb radiation in the `window' through which energy normally escapes into space.
This leads to an enhanced global warming effect. The majority of scientists now believe human
activity is contributing to global warming.…read more

Page 3

Preview of page 3

Here's a taster:

The atmosphere is divided into three sections ­ the troposphere, the stratosphere and the
ionosphere. The troposphere, the section closest to the Earth's surface is made up of about 78%
nitrogen and 21% oxygen. The remaining 1% is a mixture of gases, mainly argon, and carbon dioxide.
Human activity alters the proportions of some of the naturally occurring gases, which then become
major pollutants e.g. carbon dioxide. Other pollutants such as chlorofluorocarbons (CFCs) occur only
as a result of human activity.…read more

Page 4

Preview of page 4

Here's a taster:

Heterolytic fission both the electrons of the shared pair go to just one of the atoms when the
bond breaks- this forms ions. H=Cl -> H+ Cl-
In Homolytic fission one of the two electrons in the shared pair goes to each of the atoms.
Both atoms now have one unpaired electron. a radical has been formed. Br=Br->2Br.
If the radical formed has two unpaired electrons it is called a biradical. an example is O2. .O-O.
Radicals are very reactive because of unpaired electrons.…read more

Page 5

Preview of page 5

Here's a taster:

Dynamic equilibrium
A chemical reaction has a forward reaction, but also a backward reaction. if the backward reaction is
significant then the reaction is reversible. When the rate of the forward reaction is the same as the
backward reaction a system is said to be in dynamic equilibrium.
Steady state
A chemical equilibrium can only be established in a closed system. In an open system, a series of
reactions can only come to a steady state.…read more

Page 6

Preview of page 6

Here's a taster:

At higher pressure and concentrations, particles are in closer proximity to each other
encouraging more frequent collisions
at higher temperatures, a much high proportion of colliding particles have sufficient energy
to react and more particles are able to overcome the activation enthalpy barrier
with smaller particles of reactant there is a larger surface area on which the reactions can
take place, so the greater the chance of successful collisions.
heterogeneous catalysts provide a surface where reacting particles may break and make
bonds.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »