Acid-base reaction equilibrium

In summary: In this case, the equilibrium constant for the reaction of NH4+ with water is -10.3 and for the reaction of HA with NH3 it is 2.7.
  • #1
Huzaifa
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2
TL;DR Summary
Equilibrium constants in acid-base reactions equations
$$
\begin{array}{c}
\mathrm{HA}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{A}^{-}+\mathrm{H}_{3} \mathrm{O}^{+} \\
\mathrm{K}=\dfrac{\left[\mathrm{A}^{-}\right]\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{\left.[\mathrm{HA}] \mathrm{H}_{2} \mathrm{O}\right]} \quad \mathrm{K}_{\mathrm{a}}=\dfrac{\left[\mathrm{A}^{-}\right]\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{[\mathrm{HA}]} \\
\mathrm{BH}^{+}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{B}+\mathrm{H}_{3} \mathrm{O}^{+} \\
\mathrm{K}=\dfrac{[\mathrm{B}]\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{\left[\mathrm{BH}^{+}\right]\left[\mathrm{H}_{2} \mathrm{O}\right]} \quad \mathrm{K}_{\mathrm{a}}=\dfrac{[\mathrm{B}]\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{\left[\mathrm{BH}^{+}\right]} \\
\mathrm{HA}+\mathrm{B} \rightleftharpoons \mathrm{A}^{-}+\mathrm{BH}^{+} \\
\mathrm{K}_{\mathrm{c}}=\dfrac{\left[\mathrm{A}^{-}\right]\left[\mathrm{BH}^{+}\right]}{[\mathrm{HA}][\mathrm{B}]}
\end{array}
$$

Hello! I am not able to understand these equations for acid base equilibrium please. I have attached the images in the following post.
 
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  • #2
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  • #3
What you posted is a definition - nothing to understand here, it just is what it is, all you have to do is to accept it - and some algebraic rearranging, that is not difficult to follow if you have a basic understanding of HS math. You have not explained what it is that you don't understand.
 
  • #4
Borek said:
What you posted is a definition - nothing to understand here, it just is what it is, all you have to do is to accept it - and some algebraic rearranging, that is not difficult to follow if you have a basic understanding of HS math. You have not explained what it is that you don't understand.
I don't understand A, B, and H, and the positive and negative signs in superscripts. I assume that A is Acid, and B is Base, and H is Hydrogen. Please correct me if I am wrong.

I also don't understand HA and BH+? Also there is no OH-.
 
  • #5
Huzaifa said:
the positive and negative signs in superscripts
These are ion charges. I suggest you you get back to basics, otherwise you won't be able understand the acid/base equilibrium.

A and B are often used as general symbols for acid (base) residue. HA means just any monoprotic acid.
 
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  • #6
The first equation shows the reversible transfer of the H+ ion from the acid HA to water H2O to form the hydronium ion H3O+ and the anion A-. The second shows the calculation of the equilibrium constant K for this reaction. Since the concentration of water is very high (~55 molar) it does not change significantly and is neglected in the calculation of the acid equilibrium constant Ka. Thus the equilibrium constant is equal to the concentration of the anion times the concentration of the hydronium ion divided by the concentration of the acid and of the water.
The second set of equations refers to the reaction of a basic salt such as the ammonium ion NH4+ with water and the third set refers to the reaction of an acid HA and a base such as ammonia NH3. These equilibrium constants cover 14 powers of ten from 101 to 10-14 so it is more convenient to use their negative logarithms: 0 to 14.
 

Related to Acid-base reaction equilibrium

What is an acid-base reaction equilibrium?

An acid-base reaction equilibrium is a chemical reaction in which an acid and a base react with each other to form a salt and water. This reaction is reversible, meaning the products can react with each other to form the original reactants.

How is the equilibrium constant determined for an acid-base reaction?

The equilibrium constant, also known as Keq, is determined by the ratio of the products to the reactants at equilibrium. It is calculated by dividing the concentration of the products by the concentration of the reactants, each raised to their respective stoichiometric coefficients.

What factors affect the position of an acid-base reaction equilibrium?

The position of an acid-base reaction equilibrium can be affected by factors such as temperature, pressure, and the concentrations of the reactants and products. Changes in these factors can shift the equilibrium towards the reactants or products, depending on the direction of the change.

How does Le Chatelier's principle apply to acid-base reaction equilibrium?

Le Chatelier's principle states that when a system at equilibrium is subjected to a stress, it will shift in a direction that reduces the stress. In the case of an acid-base reaction equilibrium, this means that when the concentration of one of the reactants or products is changed, the equilibrium will shift to counteract the change and maintain the equilibrium constant.

What is the significance of acid-base reaction equilibrium in everyday life?

Acid-base reaction equilibrium plays a crucial role in many everyday processes, such as digestion, cleaning, and water treatment. It also helps to maintain the pH balance in our bodies and in the environment, ensuring that chemical reactions can occur efficiently and effectively.

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