Page 39 - Curriculum Visions Dynamic Book

ozone: a form of oxygen whose molecules contain three atoms of oxygen. Ozone is regarded as
a beneficial gas when high in the atmosphere because it blocks ultraviolet rays. It is a harmful gas when breathed in, so low level ozone, which is produced
as part of city smog, is regarded as a form of pollution. The ozone layer is the uppermost part of the stratosphere.
stratosphere: the part of the Earth’s atmosphere that lies immediately above the region in which clouds form. It occurs between 12 and 50 km above the Earth’s surface.
This very reactive chlorine atom is called
a “free radical”. It can now react with another ozone molecule, causing further destruction of the ozone layer.
+➡
A refrigerator works by taking heat from one part of its surroundings, and giving it out elsewhere. In general, refrigerators take heat from the area inside them, near the ice box, and give it out to the room through a network of pipes fixed to the back of the refrigerator.
To act as a refrigerant, the liquid used has to be pumped around a system of closed tubes. The liquid is made to boil inside the refrigerator and to condense outside.
The liquid chosen has to be able to get very cold inside the refrigerator (so that is can take up heat from the air in the ice compartment), and get very hot outside it (so it can give heat out to the surroundings). Ammonia is one common gas that could be used, but the inert (nonreacting) properties of CFCs are preferable.
EQUATION: Reaction of CFCs with ozone
 CFC + ultraviolet light ➪ chlorine CFC(g) + UV light ➪ Cl(g)
 Chlorine atom + ozone ➪ chlorine oxide + oxygen Cl(g) + O3(g) ➪ ClO(g) + O2(g)
 Chlorine oxide + oxygen atom ➪ chlorine atom + oxygen
ClO(g)
A chlorine (Cl) atom is released from CFCs and carried into the upper atmosphere by air currents.
+ O(g) ➪ Cl(g) + O2(g)
+➡+
Ozone (O3) molecules are formed in the upper atmosphere.
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How refrigerants work
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 The first CFC-free substitutes are now being produced. This one is called KLEA.