CHEM 1A03 LECTURE 6 – DYNAMIC CHEMICALEQUILIBRIUM
October 9-14 2012
Equilibrium Constant (K)
K is a thermodynamic parameter characterizing the tendency for a chemical rxn or process to
Chemical process are reversible – the extent of rxn is determined by L
K is a ratio of product to reactant ACTIVITIES (a) – effective concentration or pressure – at llbm.
The form of K depends on the balanced chemical equation:
K = [REACTANTS] to the powers of their respective numerical coefficients
The activity (a) of a solute S is given by a = y[S]/[S]o
• where [S] o 1mol/L is the reference state.
• Y is the activity coefficient; assume y=1 (it is under “ideal conditions” – conc < 0.001M)
The activity (a) of a gas G is given by a = y*P /g o
• Use a = P (go units) where P = 1otm is the reference state; assume y=1
The activity (a) of a pure solid of liquid is 1 – This means you can ignore them when setting up
the equilibrium constant
Reserve the subscript on K to denote the type of rxn.
K expression MAY include concentrations (aw) and/or pressures (gases)
K spdissolution rxns K – cctivities are concentrations K – acpivities are partial pressures. Reaction Quotient (Q)
K = ratio of products/reactants at llbm (constant at a given temperature)
Q = ratio of products to reactants at ANY INSTANT (can hold any balue)
If Q < K Reaction proceeds forwards
If Q > K Reaction moves backwards If Q = K llbm is established.
Octanol Water Partition coefficient
K owis the octanol-water partition coefficient and gives a measure of lipophilicity of a solute (S)
If a beaker has water