The equilibrium constant Kc

What is the equilibrium law used to do?

Calculate the exact position of equilibrium by using the concentrations of everything

Which factors of the following affect the equilibrium constant and which don’t?

• Temperature

• Pressure

• Catalyst

• Starting amounts of chemicals

Affects:

• Temperature

Doesn’t affect:

• Pressure

• Catalyst

• Starting amounts of chemicals

For the following general reversible reaction, write the equation for the equilibrium constant K_c:

aA +bB ⇌ cC +dD

Give the expression for K_c for the following:

N_2(g) + O_2(g) ⇌ 2NO_(g)

What does K_c tell us?

The relative proportions of reactants and products in the equilibrium system

What does K_c = 1 mean?

Position of equilibrium is halfway between reactants and productsW

What does K_c > 1 mean?

Position of equilibrium is towards the products

What does K_c < 1 mean?

Position of reactants is towards the reactants

How is the units of K_c determined?

The units of K_c depend on the number of concentration terms on the top and bottom of the equilibrium constant term:

1. Substitute units into the expression for K_c

   1. Cancel common units and show the final units on a single line (put positive indices before negatie indices)

What should be noted when calculating K_c for heterogeneous equilibria?

Any solids or liquids are omitted - concentrations of these are essentially constant

• K_c only includes (g) or (aq)