Kb: NH3+H2O<=>NH4++OH-: Why Omit H2O?

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SUMMARY

The discussion centers on the equilibrium expression for the reaction NH3 + H2O ⇌ NH4+ + OH-. It clarifies that while H2O is typically included in the equation for Kb, it can be omitted in acid-base reactions involving NH4+. The dissociation constant for NH4+ is 5.6×10-10, confirming that NH4+ can act as a weak acid. The conversation also touches on the relationship between equilibrium constants and the substitution of OH- with Kw/H+.

PREREQUISITES
  • Understanding of acid-base equilibrium concepts
  • Familiarity with dissociation constants and their significance
  • Knowledge of the Bronsted-Lowry theory of acids and bases
  • Basic grasp of equilibrium constant calculations
NEXT STEPS
  • Research the implications of omitting solvent in equilibrium expressions
  • Study the dissociation constants of weak acids and bases
  • Learn about the relationship between Kw, H+, and OH- concentrations
  • Explore the Bronsted-Lowry theory in greater detail
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Chemistry students, educators, and professionals interested in acid-base reactions and equilibrium concepts will benefit from this discussion.

alingy1
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Why is it that for the constant Kb, we always have to write H2O in the equation and we can omit H2O in acid reactions:

My textbook always writes:
NH3+H2O<=>NH4++OH-
NH4+<=>NH3+H+

Why can we not write NH3+H+<=>NH4+?
 
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alingy1 said:
Why can we not write NH3+H+<=>NH4+?

We can. NH4+ is a weak acid, with a dissociation constant of 5.6×10-10, and above dissociation reaction is perfectly valid.

Your book my be sticking to one convention to make things easier to follow.
 
Would the equilibrium constant be the same of that reaction? Or should we substitute OH- with Kw/H+?
Kw=10^-14
 
I guess this means yes. :)
 

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