Chemical Equilibrium Q, K, and Calculations Chapter 16

Equilibrium the forward and reverse reactions proceed at equal rates the concentrations of reactants and products are constant = Can be reached from either direction (starting with either “reactants” or “products” has the same result) CO + 3H 2 CH 4 + H 2 O Example Reaction

CO + 3 H 2 CH 4 + H 2 O

Q and K Reaction Quotient: Q –Describes a rxn at _____________ Equilibrium Constant: K –Describes a rxn at _____________ Both values are calculated from the same expression

c a A(aq) + b B(aq) c C (aq) + d D(aq) For a general reaction occurring __________: [ ] = molarity Equilibrium Constant Expression

Equilibrium Constant Expressions The exponents are based on the __________!! ________ OVER _______ There are no _____ for Q or K When writing the expressions Include only these phases: ___ + ____ Omit these phases: ____+ ____

For reactions of __________: K p = P C P D P A P B c d a b P = partail pressure of the gas a A(g) + b B(g) c C (g) + d D(g)

Q and K If concentrations or partial pressures represent the reaction at equilibrium, you can calculate ______. If concentrations or partial pressures represent the reaction at any time, you can calculate ______.

Write the equilibrium expression 1) N 2(g) + 3H 2 (g) 2NH 3 (l) (K p ) 2) CO (g) + 3H 2(g) CH 4(g) + H 2 O (g) (K c & K p )

2 Red(g) Blue (g) Write the expression for K c and K p Applet

PCl 3 (g) + Cl 2 (g) PCl 5 (g) K c = [PCl 5 ] [PCl 3 ][Cl 2 ] Different amounts of R & P are mixed at 546 K to determine K Calculating K Comment on the equilibrium position.

Calculating K H 2 (g) + I 2 (g) 2HI At equilibrium, the concentration for both H 2 and I 2 = M and HI = Write the expression for K and calculate its value? What this value mean? K > 1 the reaction is ________ favored K< 1 the reaction is ________ favored

Calculating Q H 2 (g) + I 2 (g) 2HI 2 moles each of H 2 and I 2 and 3 moles of HI are placed in a 0.5 L flask. Determine if the rxn is at equilbrium? If not will it move forward or reverse? Q = K the reaction _______________ Q < K the reaction ________________ Q > K the reaction ________________

K c and K p are related K p = K c (RT) ∆n R= Liter atm mol K ∆n = # product gases - # reactant gases

H 2 (g) + I 2 (g) 2HI If K c = 56, calculate K p at 25 °C. K p = K c (RT) ∆n

A real one! K p = K c (RT) ∆n N 2 (g) + 3 H 2 (g) 2NH 3 (g) The Kp = 5.8 x10 5, calculate K c at 25 ° C.

MORE ABOUT K!!!! K values for various forms of a balanced equation relate to the coefficients The K value for the reverse rxn is the ______________ Multiplying a reaction by a # _______________

MORE ABOUT K!!!! at 298 K C(s) + 1/2 O 2 (g) CO(g) K 1 = 4.6 X C (s) + O 2 (g) 2CO(g) K 2 = ?

MORE ABOUT K!!!! When adding reactions to produce a net equation, ________ K values. For a 2 reactions, with K 1 and K 2, K net = K 1 K 2