Everything Science Grade 12

3.8 CHAPTER 3. REACTION RATES

Conclusions:

Use your knowledge ofequilibrium principles to explain the changes that

you recorded in the table above. Draw a conclusion about the effect of a

change in concentrationof either the reactants or products on the equilibrium

position. Also draw a conclusion about the effect of a change in temperature

on the equilibrium position.

The effect of pressure onequilibrium ESCBF

In the case of gases, werefer to pressure insteadof concentration. Similar principles
apply as those that were described before for concentration. When thepressure of a
system increases, thereare more particles in aparticular space. The equilibrium will
shift in a direction that reduces the number of gas particles so that the pressure is also
reduced. To predict what will happen in a reaction, we need to look atthe number of
moles of gas that are inthe reactants and products. Look at the examplebelow:

e.g. 2 SO 2 (g) + O 2 (g)� 2 SO 3 (g)

In this reaction, two moles of product are formed for every three molesof reactants. If
we increase the pressure on the closed system,the equilibrium will shift to the right
because the forward reaction reduces the number of moles of gas that are present. This
means that the yield ofSO 3 will increase. The opposite will apply if the pressure on
the system decreases. The equilibrium will shift to the left, and the concentration of
SO 2 and O 2 will increase.

Example 6: Reaction Rates 1

QUESTION

2 NO 2 (g)� 2 NO (g) + O 2 (g). ΔH > 0. How will the rate ofthe reverse

reaction be affected by:

1. A decrease in temperature?


2. The addition of a catalyst?


3. The addition of moreNO gas?