15.1b Equilibrium Constant, K c

created in 1864 by Guldberg and Waage (Norweigen) for a reaction: aA + bB ⇄ cC + dD equilibrium constant: K c

always use a balanced equation with whole number coefficients when using equilibrium law the greater the K c value the more the products are favoured at equilibrium both temperature and concentration changes can effect the value of K c K c only provides a measure of equilibrium position and not info on reaction rates

will always have the same value at a certain temperature no matter what amounts are added ratio at equilibrium will always be same Since equilibrium depends on concentrations, these substances must be expressed as they exist ions in solution are written as net ionic equations

each set of equilibrium concentrations depends on initial concentrations

involves more than one phase position of heterogeneous equilibrium does NOT depend on amounts of: pure solids pure liquids because their concentrations stay constant (since they are PURE)

do not include liquids or solids in equilibrium expression only include gases and solutions (aq)

Write the equilibrium expression for: 2H 2 O (l) ⇄ 2H 2 (g) + O 2 (g) Write the equilibrium expression for: 2H 2 O (g) ⇄ 2H 2 (g) + O 2 (g)

Write the equilibrium expression for: 4NH 3 (g) + 7O 2 (g)  4NO 2 (g) + 6H 2 O (g) What would it be for the reverse reaction?

Text p688 #1-4 LSM 15.1C summary