Help - Confusion acid-base equilibrium in water

[mcfaker123]

Help -- Confusion acid-base equilibrium in water

Hello,
I have been reading about the acid-base equilibrium in water. I don't understand what my book explains however. The theory may be information lacking(in my opinion). Because I've read it so many times I just decided to rewrite everything exactly from my book! I also "rewrote" 2 examples after the theory. I am also confused about what they try to accomplish in the examples. I figure they try to set up the reaction of the acid-base equilibrium in water. In the second example they marked H3O+ & OH- in red, I don't know what that means though. Then next to "simplified" they let H3O+ react with NH3. How do I know whether H3O+ reacts with NH3 or with OH-? And why is it H3O+ that reacts with NH3 and not for example Cl- that reacts with H20 or NH4+?

Im really confused with this material in my book & can't get out of it no matter what. Can anyone please help me?

Thanks in advance!

Theory:

Example 1:

Example 2:

 

[Asim Riaz]

The acid-base equilibrium in water is the balance between the acid and base molecules in aqueous solutions. Acids are molecules that donate hydrogen ions (H+) to a solution, while bases accept hydrogen ions. This process creates an equilibrium, meaning that the concentrations of both the acid and base molecules remain constant. In an aqueous solution, the equilibrium is represented by the following equation: H2O + H+ <=> H3O+ + OH- This equation states that there is an equilibrium between the water molecules (H2O) and the two ions created when they react, hydrogen ions (H+) and hydroxide ions (OH-). The equilibrium is expressed as an equilibrium constant, K_eq. Example 1: Let's say we have an aqueous solution of hydrochloric acid (HCl). HCl dissociates into H+ and Cl- ions when it is dissolved in water, so the equilibrium is represented by the following equation: H2O + HCl <=> H3O+ + Cl- Example 2: Let's say we have an aqueous solution of ammonia (NH3). NH3 dissociates into NH4+ and OH- ions when it is dissolved in water, so the equilibrium is represented by the following equation: H2O + NH3 <=> H3O+ (red) + OH- (red) Simplified: H3O+ (red) + NH3 <=> NH4+ + OH- (red) In this equation, H3O+ reacts with NH3 and forms NH4+ and OH-. The OH- is the same as the OH- from the original equation.