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If the volume is increased by 2, then the concentration of each of the

reactants is reduced by 2 times. At new concentrations, the speed of the direct

reaction (υ'):

2
2
υ' = k [1⁄2 СO] · [1/2 О 2] = 1⁄8 k [СО] [O 2]

Consequently, the direct reaction velocity will be reduced by 8 times.

Example 3. How does the speed of the direct reaction change?

Fe 2O 3(hard) + 3H 2(gas) → 2Fe(hard) + 3H 2O(gas),

if the initial pressure in the system is increased by three times?

Solution:

Prior to the pressure changing in the system the reaction rate:
3
υ = k [H 2]

With increasing pressure by three times the concentration of the reactants will
increase by 3 times. At new concentrations, the reaction rate (υ '):

3
3
υ' = k [3H 2] = 27 k [H 2] .
Consequently, the reaction rate will increase by 27 times.

Example 4. The reaction of the decomposition of phosphorus pentachloride has

the following equation:

РСl 5(gas) ↔ РСl 3(gas) + Сl 2(gas) – 92 KJ

How should:

a) the temperature;

b) the pressure;

c) the concentration of reagents be changed to shift the reaction equilibrium

toward the decomposition of РСl 5 (to the right).

Solution. The direction of the displacement of the reaction equilibrium is

determined by Le Chatelier’s principle: a) since the decomposition reaction of the

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