Chem ch 14

chemical equilibrium

the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant

equilibrium constant

K = products over reactants raised to the power of their coefficientsit is a dimensionless quantity(unlike little k), don't worry about whyconstant values unless temperature changesIf K<<1 - the denominator is much larger than the numerator, therefore the reactants are favoredIf K >> 1 the equilibrium "lies to the right"if you flip the reaction, invert K (4.0 --> 0.25)

homogeneous equilibria

all reacting species are in the same phaseall are gassesall are aqueous

heterogeneous equilibria

reacting species exist in different phasessolids & gasessolids & liquidsdon't include solids (s) and liquids (l) in the equilibrium constant only gases (g) or solutions (aq)

relationship between Kc and Kp

PV = nRT......soKp = Kc (RT)^ (to the power of the change in n)

Dynamic Equilibrium

in a reversable reaction reactants are always turning into products and products are always turning into reactants

Le Chatelier's Principle

if an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset*if adding a gas that doesn't appear in the balanced equation, it has no effect on equilibrium

law of mass action

for a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentrations has a constant value (K)

multiple equilibria

if a reaction can be expressed as the sum of 2 or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions (Hess's law) Kc = Kc' x Kc

catalyst

lowers the activation energy for the forward and the reverse reaction to the same extentdoesn't alter the equilibrium constant, nor shifts the equilibrium

How does temperature affect equilibrium?

temperature increase favors an endothermic reaction (+^H) - reactants + heat <=> productstemperature decrease favors an exothermic reaction (-^H) - reactants <=> products + heat

reaction quotient Q

same form as K but is not at equilibriumif Q < K the reaction must go forward (to the right) (form products) to reach equilibriumif Q = K the reaction is at equilibriumif Q > K the reaction must go backward (left, reactants) to reach equilibrium