Gay Lussac’s of combining volumes states that gases react in simple ratio with one another and to volumes of the products provided that temperature and pressure remain constant. In this article, you will understand how to apply this law in calculation by studying the following examples below: 1. 2H 2 + O 2 → H 2 O In the reaction above, what volume of hydrogen would be left over when 300cm 3 of oxygen and hydrogen are exploded in a sealed tube? 1cm 3 of oxygen = 2cm 3 of hydrogen 300cm 3 of oxygen = 2 x 300 = 600cm 3 Volume of left over = 1000 – 600 = 400cm 3 2. Calculate the volume of carbon (II) oxide required to react with 40cm 3 of oxygen. 2CO + O 2 → 2CO 2 1cm 3 of oxygen = 2cm 3 of CO 40cm 3 of oxygen = 2 x 40 = 80cm 3 3. Calculate the volume of residual gases that would be produced when 100cm 3 of sulphur (IV) oxide reacts with 20cm 3 of oxygen 2SO 2 + O 2 → 2SO 3 1cm 3 of O 2 = 2cm 3 20cm 3 of O 2 = 2 x 20 = 40cm 3
The collision theory shows that the rate of a chemical reaction depends on the frequency of the effective collisions between reactant particles. So any factor that can influence one or all following
·
The energy content of the particles
·
The frequency of the collision of the particles
·
The activation energy of the chemical reaction
Can also affect the rate of chemical rate and such factors
are
·
Nature of reactants
·
Concentration / pressure(for gas) of the reactants
·
Surface area of reactants
·
Temperature of reaction mixture
·
Presence of light
·
Presence of catalyst
Nature of Reactants:
The rate of reaction is affected by the chemical nature of the reactants
because the energy content of different substances is not the same. For example,
zinc reacts very fast with dilute hydrochloric acid to liberate hydrogen while
gold does not show any sign of reaction.
Concentration of
reactants: The frequency of collision increases with an increase in concentration,
for gas, an increase in pressure increases the frequency of collision, while the decrease in concentration or pressure (for gas) decreases the frequency of
collision of the reactant particles.
The surface area of the
reactants: powdered marble chips react faster with dilute hydrochloric acid
than granules. This is because the powdered marble chips have increased surface area
in contact with the acid.
Temperature:
Reactions are faster at high temperatures and slower at low temperatures. The increase
in temperature of a system can lead to an increase in the rate of chemical reaction
in two ways;
·
By increasing the energies of particles more
than or equal to the activation energy
·
By increasing the average speed of all the reactant
particles due to increased kinetic energy
These ways increase the number of effective collisions and
help the reaction to be faster.
Light:
Photochemical reaction like the reaction between hydrogen and chlorine is explosive
in the presence of bright sunlight but negligible in the absence of light.
Catalyst: This is
a substance that can change the rate of a chemical reaction without undergoing
any change at the end of the reaction. Some catalysts can promote the rate of
response while some retard the reaction.
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