Indicate the correct answer out of the following for the reaction: + ⇌ + : — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

Step 1 - Convert the Molecular Equation to Net Ionic Form The given reaction represents the hydrolysis of ammonium chloride (\ce{NH4Cl}), which is a salt of a weak base (\ce{NH3} / \ce{NH4OH}) and a strong acid (\ce{HCl}): \[\ce{NH4Cl(aq) + H2O(l) <=> NH4OH(aq) + HCl(aq)}\] Since \ce{NH4Cl} and \ce{HCl} are strong electrolytes in aqueous solution, they dissociate completely into their respective ions: \[\ce{NH4+(aq) + Cl-(aq) + H2O(l) <=> NH4OH(aq) + H+(aq) + Cl-(aq)}\] Canceling the spectator chloride ion (\ce{Cl-}) from both sides yields the net ionic equation for the hydrolysis: \[\ce{NH4+(aq) + H2O(l) <=> NH4OH(aq) + H+(aq)}\] Here, the hydrogen ion (\ce{H+}) and ammonium hydroxide (\ce{NH4OH}) are the products of the forward reaction. Step 2 - Apply Le Chatelier's Principle to Analyze the Perturbations According to Le Chatelier's Principle, if a constraint (such as a change in concentration, temperature, or pressure) is applied to a system at equilibrium, the equilibrium will shift in a direction that tends to counteract or minimize the effect of that constraint: * Adding a reactant or removing a product shifts the equilibrium in the **forward direction** (favours the reaction). * Adding a product or removing a reactant shifts the equilibrium in the **backward direction** (retards the reaction). Step 3 - Evaluate Option (A): Addition of Potassium Hydroxide (\ce{KOH}) * Potassium hydroxide (\ce{KOH}) is a strong base that dissociates completely in water: \[\ce{KOH(aq) -> K+(aq) + OH-(aq)}\] * The added hydroxide ions (\ce{OH-}) immediately react with the product hydrogen ions (\ce{H+}) in a highly favorable neutralization reaction to form water: \[\ce{H+(aq) + OH-(aq) -> H2O(l)}\] * This consumption of \ce{H+} drastically decreases the concentration of one of the products. * To counteract this decrease, the equilibrium shifts in the **forward direction** to produce more \ce{H+}. Hence, addition of \ce{KOH} **favours** the reaction, rather than retarding it. Therefore, Option (A) is incorrect. Step 4 - Evaluate Option (B): Addition of Ammonium Hydroxide (\ce{NH4OH}) * Ammonium hydroxide (\ce{NH4OH}) is a direct product of the forward reaction. * Introducing extra \ce{NH4OH} increases the concentration of the products. * To counteract this increase, the system shifts in the **backward direction** to consume the excess \ce{NH4OH}. Hence, addition of \ce{NH4OH} **retards** the reaction, rather than favouring it. Therefore, Option (B) is incorrect. Step 5 - Evaluate Options (C) and (D): Addition of Hydrogen Ion (\ce{H+}) * Hydrogen ion (\ce{H+}) is a product of the hydrolysis reaction. * Increasing the concentration of \ce{H+} by adding an acid increases the product concentration. * To counteract this stress, the equilibrium shifts in the **backward direction** to consume the excess \ce{H+}. * Consequently, the forward reaction is **retarded** (slowed down). Therefore, Option (C) is correct, and Option (D) is incorrect. \[\boxed{\text{C}}\]