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 Form 4 Chemistry lessons on reaction rates and reversible reactions

Application of effect of light on reaction rate and effect of pressure on rate of reaction

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Answer Text:
Application of effect of light on reaction rate.
- Processing of black and white photographic films is done in dark to prevent the decomposition of the silver bromide that is usually used to coat photographic plates; Further examples of reactions affected by light:
#Cl_2(g)+H_2(g) overset(UV. light)(to) 2HCl(g)#
#CH_4(g)+ Br_2(g) overset(UV. light)(to) CH_3Br(g)+HBr(g)#
#6CO_2(g)+ 6H_2O(l)overset(light)(to)C_6H_12O_6(aq)+6O_2(g)#
(f). Pressure
- Increase in pressure increases the rate of reaction involving the formation of small volume of product because of increase in concentration and slight
increase in temperature
- In a given volume the higher the number of molecules of a given gas in a container, the greater the pressure;
- Increase in pressure causes the same effect as increase in concentration;
- Thus the rate of reactions involving gases can be increased by increasing the pressure of the gases
Note:
From gas laws, decreases in volume results in increase in pressure. Thus, reactions accompanied by decrease in volume move faster to completion.


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