Page 29 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

➢ At equilibrium, the two opposing rates will be equal therefore r1 = r2
a b c d
K . [A] .[B] = K .[C] .[D]
1 2

= [ ] [ ] Keq = [ ] [ ]

[ ] [ ] [ ] [ ]

K / k is constant → K
1 2 eq
(Keq): Equilibrium constant

• The equilibrium constant, K , is the ratio of
eq

the equilibrium concentrations of products
over the equilibrium concentrations of reactants each raised to the power of

their stoichiometric coefficients.
• Example. Write the equilibrium constant, K , for:
eq

N O (g) ⇌ 2NO (g)
2 4 2

[ ]

=
[ ]

Le Chatelier's Principle

“If a stress is applied to a system in equilibrium, the equilibrium tends to
shift in a direction to neutralize the stress”.

Factors affecting the reaction equilibrium (direction):

1. Temperature

2. Pressure

3. Concentration (common ion effect)

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