Equilibrium Superdoc

Part 1 Packet

General Stuff About equilibrium

  • Equilibrium concentrations do not have to be equal to one another

  • chemical equilibrium: rate of fwd and reverse reactions are equal

    • amount of reactants and products are CONSTANT @ equilibrium unless its disturbed

  • Keq is unitless

K

  • K > 1: Reaction is product favored

    • concentration of products are much greater than concentration of reactants @ equilibrium

  • K < 1: Reaction is reactant favored

    • concentration of reactants are much greater than concentration of products @ equilibrium

  • Think of like a number line (left, K is less, reactants)

Q vs K

  • Q = K, @ equilibrium

  • Q > K, too many products, net reaction proceeds to the reactants

  • Q < K, too many reactants, net reaction proceeds to products

    • ALWAYS WRITE Q THEN K, WHEREVER THE OPEN SIDE GOES IS WHERE THE REACTION PROCEEDS

  • Remember that with FRQ problems with Q and K, don’t say shift

    • say that the EQUILIBRIUM PROCEEDS

Rxn Mechanisms

  • Remember the substituting for the rate with the intermediates?

    • if a step of the reaction mechanism is at equilibrium, isolate and solve for the concentration of the intermediate and plug it into the rds

Homogenous Equilibria

  • all reactants and products are in same phase

  • Gas Phase:

    • eq constant can be expressed in terms of concentration or partial pressures

  • if volume of a reactant/product is so large → you can define the concentration as constant

Relationship btwn Kp and Kc

  • PV = nRT

  • C = n/V = P/RT

    • P = CRT

Concentration of a solid/pure liquid

  • substitute 1 for the concentration of a solid or pure liquid

Heterogeneous Equilibrium

  • reversible rxn where reactants and products are in different phases

Multiple Equilibria

  • Add the Reactions: If the overall reaction is obtained by adding the two individual reactions, then the equilibrium constant for the overall reaction is the product of the equilibrium constants of the individual reactions.

    • Koverall​=K1​×K2​

  • Subtract the Reactions: If the overall reaction is obtained by subtracting one reaction from another, then the equilibrium constant for the overall reaction is the quotient of the equilibrium constants of the individual reactions.

    • Koverall = K1/K2

  • Multiply or Divide by a Factor: If a reaction is multiplied by a factor nn, the equilibrium constant is raised to the power of nn.

    Knew=KnKnew​=Kn

  • Reverse the Reaction: If a reaction is reversed, the equilibrium constant is the reciprocal of the original equilibrium constant.

    Knew=1KKnew​=K1​

Example

Le Chateliers

Concentration

Volume

  • equilibrium will shift to side of reaction with

    • fewer moles of gas if volume is reduced to offset increased pressure

    • greater moles of gas is volume is increased to offset decresaed pressure

Temperature

  • consider if rxn is endo or exothermic

    • Endothermic

      • energy is absorbed when rxn runs in fwd direction (think of energy as a reactant)

      • Kc increases when temperature is raised and vice versa

    • Exothermic

      • energy is absorbed when rxn runs in reverse direction (think of energy as a product)

      • Kc decreases when temperature is raised and vice versa

Temperature changes how the fuck does K change