Equilibrium Constants - Summary Sheet

I Produced this summary sheet for all the equilibrium constants. It basically explains all the different equations. I hope you find it useful.

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  • Created by: Gugan
  • Created on: 07-11-09 17:16
Preview of Equilibrium Constants - Summary Sheet

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Concentration Constants
equilibrium constant (kc) = [[reactants
Pressure Constants
equilibrium constant (kp) = pp (reactants)
Strong & Weak Acids & Bases
A strong acid is an acid which is totally ionised in aqueous solution forming hydrate hydrogen
ions, H3O+
A weak acid is an acid that is only very slightly ionised in aqueous solution
A strong base is totally ionised in aqueous solution forming hydroxide ions, OH-
A weak base is protonated to only a small degree in solution and so only forms a small
proportion of hydroxide ions
Acid Dissociation Constants
An acid is a substance that can accept the pair of electrons from a base and for a bond.
i.e. an acid donates an electron e.g.
HA + H2O H3O+ + A-
acid dissociation constant (ka) = [HA]
Base Dissociation Constants
A base is a substance which has a lone pair of electrons, which it uses to form a covalent
i.e. a base accepts an electron e.g.
NH3 + H2O NH4+ + OH-
[NH4 ][OH-]
base dissociation constant (kb) = [NH3]
Water is not included in the equations because the concentration of water is
constant in aqueous equilibria involving weak acids & bases
Water Constants
Water is amphoteric i.e. can be an acid or a base.

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H2O + H2O H3O + + OH-
I onic product of water (kw) = [H +][OH - ]
pH Scales
pH =- log[H +]
[H +] = e-pH
pKw, pOH & pKa
p means `the negative log of'
pK w =- logK w K w = pH + pOH = 14
pOH =- log[OH-]
pK a =- logK a K a = e-Ka
pH of Strong Acids
Strong acids dissociate almost completely so you simply use the pH equation to find the pH
of a…read more

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The pH of weak acids can be calculated in the same way as the acid dissociation constant.
acid dissociation constant (ka) = [HA]
You would use the concentration at equilibrium.
Diprotic acids would produce two hydrogen ions per molecule e.g. sulphuric acid.
pH of Weak Bases
The pH of weak bases can be calculated by first calculating the concentration of the
hydroxide ions.…read more


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