Dynamic Equilibrium Chapter 15. Example liquid + heat vapour an endothermic physical change. Le Chatelier’s Principle. When a dynamic equilibrium is upset by a disturbance, the system responds in a direction that tends to counteract the disturbance and, if possible, restore equilibrium.
liquid + heat vapour
an endothermic physical change
liquid + heat
Increase the temperature (add heat)
liquid + heat
Liquid evapourates to absorb the added heat and the position of the equilibrium shifts to the right
CH3COOH + H2O H3O++CH3COO-
For a given composition of a system, equilibrium is independent of which side you approach it from…..reactions are REVERSIBLE
Cinit 0.0350 mol 0
or 0 0.0700 mol
Cequil 0.0292 mol 0.0116 mol
H2(g) + I2(g) 2HI(g) (at 440C)
Mass action expression:
Where Q is the reaction quotient
LAW: at equilibrium the reaction quotient is equal to the equilibrium constant, K.
In general for
dD + eE gG + hH
For gaseous reactions use partial pressures, P, to give an equilibrium constant (Kp)
products are present at equilibrium.
reactants are present at equilibrium.
at equilibrium and equilibrium lies
to the right.
at equilibrium and the equilibrium
lies to the left.
Adding or removing reactant or product
Cu(H2O) 42+(aq.) + 4Cl-(aq.) CuCl 42-(aq.) + 4H2O
Changing volume (or pressure)-gases only
as liquids and solids are incompressible
Decrease V=>increase P
System opposes this by reducing the number of molecules
Changing temperature (heat)
System opposes this by trying to absorb the added heat
ONLY factor that actually changes the value of K
Effect of catalyst
Speeds up approach to equilibrium, but does not
alter K or the system (kinetics)