3.8 EQUILIBRIUM CONSTANS

Dynamic equilibrium

Reversible reaction where rates of forward and reverse reactions are equal

Kc and Kp Exothermic

Heat is a product

Increase temperature

• shift LEFT (remove heat)

• Kc/Kp decreases

Decrease temperature - favours exothermic side

• shift RIGHT

• Kc/Kp increases

Kc and Kp Endothermic

Heat is a reactant

Increase temperature - favours endothermic side

• Shift RIGHT

• Kc/Kp increases

Decrease temperature

• Shift LEFT

• Kc/Kp decreases

Kc

Equilibrium constant terms of concentration in solutions

Kp

Equilibrium constant terms of partial gas pressure

Calculating Kc

aA + bB = cC +dD

Kc = [C]^c[D]^d / [A]^a[B]^b

Calculating Kp

Kp = (pC)^c(pD)^d / (pA)^a(pB)^b

Calculating partial pressure

pp = mole fraction x total pressure

Magnitude of Kc Kp

K>1 Products favoured (higher conc products at equilibrium)

K<1 Reactants favoured (higher conc reactants at equilibrium)

K=1 Mixture of both

• Large k→ lies to right

• Small K → lies to left

K tells you..

Position of equilibrium

Explain why powers included in calculations

Powers correspond to stoichiometric coefficients

Reflects ration in which substances react and formed

How does weak acid and its sodium salt maintain pH

RCOOH = RCOO- + H+

RCOONa = RCOO- + Na+

H+ removed by salt A^- + H⁺ →HA

OH^- removed by acid OH^- + HA → A^- + H₂O