Changing Pressure

Introduction

• Altering the pressure of an equilibrium mixture can impact the equilibrium position, especially when gaseous substances are involved.
• The shift in equilibrium depends on the change in total gas volume.

Increasing Pressure

• An increase in pressure favours the side with the lower gas volume.
• Consider the reaction between sulfur dioxide (SO₂) and oxygen (O₂) to form sulfur trioxide (SO₃).
• 2SO₂(g) + O2(g) 2SO3(g)
• On the left side of the equation, there are three moles of gaseous reactants (2SO₂ + O2), while on the right side, there are two moles of gaseous products (2SO₃).
• Increasing the pressure would shift the equilibrium to the right, favouring the formation of more sulfur trioxide (SO₃).

Pressure Unaffected Reactions

• Some reactions are not affected by changes in pressure because both sides of the equilibrium have the same total gas moles.
• For example, the reaction between hydrogen (H₂) and iodine (I₂) to form hydrogen iodide (HI) has two moles of gases on both sides.
• H₂(g) + I₂(g) 2HI(g)
• Changing the pressure in such reactions does not favour either side of the equilibrium.

Conclusion

• When dealing with gaseous equilibrium, changing pressure can influence the equilibrium position.
• An increase in pressure favours the side with fewer gas moles, while reactions with equal gas moles on both sides are pressure-independent.
• Understanding the effect of pressure is crucial for controlling reactions involving gases, such as industrial processes.