Whats the difference between activity and concentration...? at what condition they become same...? Why do we need activity at all..? why cant we simply use concentration...??

Question

anonymous · Answer

Activity and Concentration
• Activity – “effective concentration”
• Ion-ion and ion-H2O interactions (hydration shell)
cause number of ions available to react chemically
("free" ions) to be less than the number present
• Concentration can be related to activity using the
activity coefficient γ, where [a] = γ (c)
we assume that activity, a, is equal to
concentration, c, by setting γ = 1 when dealing with
dilute aqueous solutions.
But ions don’t behave ideally . . .
• Concentration related to activity using the activity
coefficient γ, where [a] = γ (c)
• The value of γ depends on:
– Concentration of ions and charge in the solution
– Charge of the ion
– Diameter of the ion
Activity coefficient γz → 1 as concentrations → 0