Consider the following chemical equation in equilibrium: [tex]$H_2 SO_4(aq) \Leftrightarrow 2 H^{+}+SO_4^{2-}$[/tex]
What will happen to the chemical equilibrium if HCl is added to the system?
A. The chemical equilibrium will be lost permanently.
B. The chemical equilibrium will not be affected.
C. The chemical equilibrium will shift to the left
Answer (2)
Adding HCl increases H + concentration.
Le Chatelier's principle dictates the equilibrium shifts to relieve this stress.
The equilibrium shifts left, consuming H + and forming H 2 S O 4 .
The chemical equilibrium will shift to the left The chemical equilibrium will shift to the left .
Explanation
Problem Analysis The chemical equation in equilibrium is: H 2 S O 4 ( a q ) i g h t ha r p oo n u p 2 H + + S O 4 2 −
Objective We need to determine what happens to the chemical equilibrium if HCl is added to the system.
Adding HCl Adding HCl to the system will increase the concentration of H + ions in the solution. This is because HCl is a strong acid and will dissociate completely into H + and C l − ions.
Le Chatelier's Principle According to Le Chatelier's principle, if a change of condition (like adding a product) is applied to a system in equilibrium, the equilibrium will shift in a direction that relieves the stress. In this case, the stress is the increased concentration of H + ions.
Equilibrium Shift To relieve the stress, the equilibrium will shift to the left, favoring the reverse reaction. This will consume the added H + ions and form more H 2 S O 4 .
Conclusion Therefore, the chemical equilibrium will shift to the left.
Examples
Le Chatelier's principle is widely used in industrial chemistry to optimize reaction conditions. For example, in the Haber-Bosch process for synthesizing ammonia ( N 2 + 3 H 2 i g h t ha r p oo n u p 2 N H 3 ), increasing the pressure shifts the equilibrium towards the product side (ammonia) because the forward reaction reduces the number of gas molecules. Similarly, controlling temperature and reactant concentrations can maximize the yield of desired products in various chemical processes. This principle helps chemists to manipulate reaction conditions to achieve the most efficient and economical production.
Adding HCl to the system increases the concentration of hydrogen ions, which causes the equilibrium to shift left in order to reduce stress. This shift results in the formation of more sulfuric acid. Therefore, the equilibrium will shift to the left.
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