Dynamic Equilibrium Chapter 15 Example liquid heat vapour

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 Increase the temperature (add heat)

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 Liquid evapourates to absorb the added heat and the position of the equilibrium shifts to the right

Chemical Equilibrium CH 3 COOH + H 2 O H 3 O++CH 3 COOFor a given composition of a system, equilibrium is independent of which side you approach it from…. . reactions are REVERSIBLE N 2 O 4(g) 2 NO 2(g) Cinit 0. 0350 mol 0 or 0 0. 0700 mol Cequil 0. 0292 mol 0. 0116 mol

Equilibrium Law simple relationship between molar concentrations (or pressures) of reactants and products at equilibrium H 2(g) + I 2(g) 2 HI(g) (at 440 C) 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 d. D + e. E g. G + h. H

Heterogeneous Equilibria (involving more than one phase)

Equilibrium Law for Gaseous Reactions For gaseous reactions use partial pressures, P, to give an equilibrium constant (Kp)

The Magnitude of Equilibrium Constants • The equilibrium constant, K, is the ratio of products to reactants. • Therefore, the larger K the more products are present at equilibrium. • Conversely, the smaller K the more reactants are present at equilibrium. • If K >> 1, then products dominate at equilibrium and equilibrium lies to the right. • If K << 1, then reactants dominate at equilibrium and the equilibrium lies to the left.

Predicting direction of equilibrium changes (Le Chatelier redux) Adding or removing reactant or product Cu(H 2 O) 42+ (aq. ) + 4 Cl-(aq. ) Cu. Cl 42 - (aq. ) + 4 H 2 O 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

Predicting direction of equilibrium changes (Le Chatelier redux) 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)