Question

Indicate how the concentration of each aqueous species in the chemical equation changes to reestablish equilibrium after changing the concentration of a reactant or product. Also indicate how the pH changes. An up arrow indicates an increase in concentration, a down arrow indicates a decrease in concentration, and leaving it blank means there is no change in the concentration. 

HCN(aq) +H₂O(l) ⇌ CN-(aq) + H₃O⁺ (aq) pH 

after the concentration of HCN is increased 

after the concentration of CN is decreased 

Answer 1

	HCN (aq)	H2O (l)		CN- (aq)	H3O+ (aq)	pH
after the concentration of HCN is increased		no change
after the concentration of CN- is decreased		no change

Explanation

According to Le Chatelier's principle, when an already established equilibrium is disturbed due to addition of a factor, the equilibrium will shift in that direction which minimizes the effect of that addition.

In first case, concentration of HCN is increased. The system moves towards products to decrease the concentration of HCN and reestablish equilibrium. This means there will be increase in the H₃O⁺ concentration and pH will decrease.

In second case, concentration of CN^- is decreased. The system moves towards products to increase the concentration of CN^- and reestablish equilibrium. This means there will be increase in the H₃O⁺ concentration and pH will decrease.

Answer 2

Answer 3

Answer 4

If the concentration of HCN increases, the law of le chatelier is fulfilled:

HCN: Increase

H2O: Decrease

CN-: Increase

H3O +: Increase

If the concentration of CN- decreases:

HCN: Decrease

H2O: Decrease

CN-: Decrease

H3O +: Increase

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