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

Concentration:

PCl3(g) + Cl2 (g) PCl5(g)

add more Cl2?

K]tstanac[Re

]oducts[Prcoeff

coeff

remove some PCl3?

Do concentration changesaffect the value of

K?

4

Pressure:

CH4(g) + 2S2(g) CS2(g) + 2H2S(g)

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

Increase pressure?

Decrease pressure?

increase pressure?

CO2(g) + C(s) 2CO(g)

increase pressure?

Do pressure changes affect

the valueof K?

5

Heat:

CO(g) + 2H2(g) CH3OH(g) Ho = - 21.7 kcal

Is this endo or exo

thermic?

Then in this case heat is a product.

So RXN is : CO(g) + 2H2(g) CH3OH(g) + heat

add Heat?

Remove Heat?

What effect doesa heat change

have on thevalue of K?

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)

K@2000K = 4.1 x 10-4 K@2500K = 36 x 10-4

So is heat a product or a reactant?

N2(g) + O2(g) + heat 2NO(g)

8

External factors affecting Equilibria:

Factor: Effect:

1. Temp Change

2. Conc. changealso pressure changes with gases

3. catalyst

value of K changes

RXN shifts to maintain value of K

since K = constant: Eq mixture is the same, but Eq is reached faster. (rate is increased)