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How does temperature affect the dissociation constant?

seo-qna
Last updated date: 20th Jun 2024
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Answer
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Hint: You must know that the dissociation of the acid in water is a reversible reaction which means the equilibrium is reached even after the condition is changed. The effect of temperature on the dissociation constant is dependent on whether the reaction is absorbing heat or releasing heat.

Complete step by step answer:
The acid dissociation constant is the equilibrium constant of the dissociation reaction of the acid. The acid dissociation is represented by ${K_a}$. It is the quantitative measure of the strength of an acid iin solution. The acid dissociation constant is measured in mol/L.
For an aqueous solution, the general form of equilibrium reaction is shown below.
$HA + {H_2}O \rightleftharpoons {A^ - } + {H_3}{O^ + }$
Here HA is an acid which dissociates in the conjugate base of the weak acid ${A^ - }$ and the hydrogen ion combines with the water to form hydronium ion.
When the concentration of the HA, ${A^ - }$and ${H_3}{O^ + }$ does not change with time, then the reaction has attained equilibrium, so the dissociation constant is given as shown below.
${K_a} = \dfrac{{[{A^ - }][{H_3}{O^ + }]}}{{[HA][{H_2}O]}}$
As dissociation is a reversible reaction so the equilibrium will be reached even when the reaction condition is changed.
The effect of the temperature on the position of equilibrium is dependent whether the forward reaction is endothermic reaction or exothermic reaction.
When the temperature is increased, the equilibrium will shift in the favour of the endothermic reaction and when the temperature is decreased then the equilibrium will shift in the favour of exothermic reaction.

Note: The acid dissociation constant is also known as acidity constant or acid ionization constant. When the acid dissociation is larger than the acid is strong and completely dissociated and when the acid dissociation is smaller than the acid is weak and it is partially dissociated.