Question

What will happen to the number of moles of SO₃ in equilibrium with and in the reaction

$\mathbf{2}\mathit{S}{\mathit{O}}_{\mathbf{3}}\mathbf{\left(}\mathit{g}\mathbf{\right)}\mathbf{\rightleftharpoons }\mathbf{2}\mathit{S}{\mathit{O}}_{\mathbf{2}}\mathbf{\left(}\mathit{g}\mathbf{\right)}\mathbf{+}{\mathit{O}}_{\mathbf{2}}\mathbf{\left(}\mathit{g}\mathbf{\right)}$

in each of the following cases?

a. Oxygen gas is added.

b. The pressure is increased by decreasing the volume of the reaction container.

c. In a rigid reaction container, the pressure is increased by adding argon gas.

d. The temperature is decreased (the reaction is endothermic).

e. Gaseous sulfur dioxide is removed.

Short answer

a. The number of moles of SO₃ will increase.

b. The number of moles of SO₃ will increase.

c. The number of moles of SO₃ will not change.

d. The number of moles ofSO₃ will increase.

e. The number of moles of SO₃ will decrease.

Step-by-step solution

Introduction

When gaseous reactants involve in a reversible chemical reaction, the amount of one of the reactants at equilibrium can be predicted by using LeChatleir’s principle.

Subpart a)

When oxygen gas is added, the product concentration is increased. This will shift the equilibrium to left to consume some of the added oxygen gas.

Subpart b)

When the pressure is increased by decreasing the volume of the reaction container, the equilibrium reaction will shift towards a fewer number of gas molecules side. In the given reaction, the reactant side has less number of moles. Hence, the number of moles of SO₃ will increase.

Subpart c)

No change is observed when the pressure in a rigid reaction container is increased by adding argon gas (inert gas, not part of this reaction). Hence, the number of moles of SO₃ will not change.

Subpart d)

When the temperature is decreased, the reaction will shift to the side of heat because heat is a reactant for the endothermic reaction. The decreasing temperature will shift this reaction to the left. Hence, the number of moles of SO₃ will decrease.

Subpart e)

The reaction will shift to the right when gaseous sulfur dioxide is removed. Since sulfur dioxide is one of the products. Hence, the number of moles of SO₃ will increase.