Summary 3.8 Equilibrium Constants

3.8 Equilibrium
Dynamic Equilibrium – When the forward and backward reaction occur at the same rate (conc. of
reactants and products remain constant but not always equal)



Changing Conditions

Le Chatelier’s Principal – If a system at equilibrium is subjected to change, the position of equilibrium
will shift to reduce the change

Concentration

- Increasing concentration of reactants or products will shift equilibrium to the opposite side
to reduce the change
- Decreasing concentration will shift equilibrium towards the same side of the reaction to
reduce the change

Pressure

- Increasing pressure will shift equilibrium to the side with fewer moles to reduce the change
- Decreasing pressure will shift equilibrium to the side with more moles to reduce the change

Temperature

- Increasing temperature shifts equilibrium to endothermic side to reduce the change
- Decreasing temperature shifts equilibrium to the exothermic side to reduce the change

Catalyst

- No effect on equilibrium position, rate of reaction is increased so equilibrium is reached
faster



Kc

At equilibrium the ratio of concentrations of reactants and products remains constant so can be put
into an expression to find the equilibrium constant (Kc)




May need to convert
moles into concentration
to use in the expression


- If Kc is large then there must be a greater proportion of products so equilibrium must lie to
the right
- If Kc is small then there must be a greater proportion of reactants so equilibrium must lie to
the left
- Kc is the equilibrium constant and only changes with temperature