CHEM 2124 – General Chemistry II
Alfred State College
Professor Bensley

 Define and describe reversible reactions.
 Define chemical equilibrium.
 Describe the equilibrium constant is and describe the meaning of the magnitude of K eq.
 Calculate the value of K eq conditions.
for given equilibrium
 Define LeChatlier’s Principle
 Describe how a system at equilibrium is affected by changing concentrations, pressure, or temperature.

Equilibrium
A. Reversible chemical reactions
The forward reaction proceeds to the right .
CO(g) + H
2
O(g) CO
2
(g) + H
2
(g)
The reverse reaction proceeds to the left .

Equilibrium
B. The equilibrium constant, K eq a A + b B c C + d D equilibrium constant
= K eq
=
[products]
[reactants]
=
[C] c [D] d
[A] a [B] b

Equilibrium
C. The Magnitude of the Equilibrium Constant
• When K eq is much greater than 1 (K eq
>> 1):
[products]
[reactants]
The numerator is larger.
• When K eq is much less than 1 (K eq
<< 1):
[products] The denominator is larger.
[reactants]
• When K eq is around 1 (0.01 < K eq
< 100): (approx.)
[products]
[reactants]
Both are similar in magnitude.

Equilibrium
D. Le Chatlier’s Principle
If a chemical system at equilibrium is disturbed or stressed, the system will react in a direction that counteracts the disturbance or relieves the stress .
Some of the possible disturbances:
• concentration changes
• temperature changes
• pressure changes

Le Ch âtelier’s Principle
Summary
7