1. Le Chatelier’s principle:
if a system at equilibrium is disturbed, the system will move in such a way as to counteract the disturbance.

2. Types of disturbances:
a. Concentration
b. Pressure - with gases, relates to concentration
c. temperature (energy)

3. Do concentration changes
PCl3(g) + Cl2 (g)  PCl5(g)
add more Cl2?
remove some PCl3?
Do concentration changes
affect the value of K?

4. Pressure:
4NH3(g) + 5O2(g)  4NO(g) H2O(g)
Increase pressure?
Decrease pressure?
Do pressure
changes affect
the value
of K?
CH4(g) + 2S2(g)  CS2(g) H2S(g)
increase pressure?
CO2(g) + C(s)  2CO(g)
increase pressure?

5. Heat:
Ho = kcal
CO(g) H2(g)  CH3OH(g)
CO(g) H2(g)  CH3OH(g) + heat
So RXN is :
add Heat?
What effect does
a heat change
have on the
value of K?
Remove Heat?
Then in this
case heat is
a product.
Is this
endo or exo
thermic?

6. Heat:
2H2O(g)  2H2(g) O2(g) H = 484 kJ
Is heat a product or a reactant?
So:
2H2O(g) + heat  2H2(g) O2(g) H = 484 kJ
add heat?
remove heat?

7. Temp. Changes:
N2(g) + O2(g)  2NO(g)
= 36 x 10-4
= 4.1 x 10-4
So is heat a product or a reactant?
N2(g) + O2(g) + heat  2NO(g)

8. External factors affecting Equilibria:
Effect:
Factor:
value of K changes
1. Temp Change
2. Conc. change
also pressure changes with gases
RXN shifts to maintain value of K
3. catalyst
since K = constant: Eq mixture is the same, but Eq is reached faster. (rate is increased)