Hydrogen chloride and oxygen react to form water and chlorine, like this 4HClg+O2g→ 2H2Og+2Cl2g Suppose a mixture of HCl,O2,H2O and Cl2 has come to equilibrium in a closed reaction vessel. Predict what change, if any, the perturbations in the table below will cause in the composition of the mixture in the vessel. Also decide whether the equilibrium shifts to the right or left.
The Correct Answer and Explanation is :
Here is the effect of different perturbations on the equilibrium composition and direction of the reaction shift based on Le Chatelier’s Principle. This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.
Reaction:
[ 4 \text{HCl}(g) + \text{O}_2(g) \rightleftharpoons 2 \text{H}_2\text{O}(g) + 2 \text{Cl}_2(g) ]
Perturbations and Effects:
- Increasing the concentration of HCl:
- Effect: The system will shift to consume the excess HCl, producing more ( \text{H}_2\text{O} ) and ( \text{Cl}_2 ).
- Equilibrium shift: Right
- Increasing the concentration of ( \text{O}_2 ):
- Effect: The system will shift to consume the excess ( \text{O}_2 ), producing more ( \text{H}_2\text{O} ) and ( \text{Cl}_2 ).
- Equilibrium shift: Right
- Removing ( \text{Cl}_2 ):
- Effect: Removing ( \text{Cl}_2 ) reduces a product. The system shifts to replace the removed ( \text{Cl}_2 ) by producing more products.
- Equilibrium shift: Right
- Removing ( \text{H}_2\text{O} ):
- Effect: Removing ( \text{H}_2\text{O} ) also reduces a product. The system shifts to replace the removed ( \text{H}_2\text{O} ) by producing more products.
- Equilibrium shift: Right
- Decreasing the volume of the container:
- Effect: Decreasing volume increases pressure. The system shifts toward the side with fewer gas moles to reduce pressure. Reactants have 5 moles, and products have 4 moles, so the equilibrium shifts to the right.
- Equilibrium shift: Right
- Adding a catalyst:
- Effect: A catalyst speeds up the reaction rate for both forward and backward reactions without affecting equilibrium composition.
- Equilibrium shift: No shift
Explanation:
Le Chatelier’s Principle helps predict how equilibrium systems respond to changes. For this reaction, shifts to the right favor product formation (( \text{H}_2\text{O} ) and ( \text{Cl}_2 )), while shifts to the left favor reactants (( \text{HCl} ) and ( \text{O}_2 )). When concentrations, volume, or pressure are altered, the system adjusts to minimize the effect of the change. For changes like adding a catalyst, equilibrium is unaffected because it influences the rate, not the composition.