Gen Chem 2

• Le Chatelier's Principle


  Whenever you impose a change on a system at equilibrium, the system will move in such a way as to undo that change or relieve some of that stress
• Le Chatelier's Principle


  1. System is at equilibrium

  2. Impose change on system

  3. System moves to undo change
• Equilibrium (chemical reaction)


  Dynamic equilibrium - the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of products and reactants remain constant
• Increase concentration of reactant B


  Reaction shifts to the right (towards products)
• Decrease concentration of reactant B

  Reaction shifts to the left (towards reactants)
• Increase concentration of product C

  Reaction shifts to the left (away from C to decrease it)
• Decrease concentration of product C

  Reaction shifts to the right (towards C to increase it)
• Increasing or decreasing any reactant or product in the solid or liquid phase will have no effect on the position of equilibrium
• Determining if reaction will shift left or right

  1. Identify if change is to reactant or product

  2. Reaction will shift to counteract the change (left for reactants, right for products)
• Actions that will cause reaction to shift left

  • Removing hydrogen gas from reaction vessel
• Actions that will cause concentration of CO to decrease


  • Removing hydrogen gas from reaction vessel
• Equilibrium


  When the rate of the forward reaction (A converting to B) is equal to the rate of the reverse reaction (B converting to A), the concentration of A and B will be constant with no net change
• Chemical equilibrium


  • It is a form of dynamic equilibrium, not static, as the reaction is still occurring even though the concentrations are not changing
• When the rate of the forward reaction equals the rate of the reverse reaction


  The concentrations of the reactants and products become constant at equilibrium
• The equilibrium constant K is equal to the ratio of the forward rate constant divided by the reverse rate constant
• Equilibrium constant K


  The ratio of the concentrations of the products divided by the concentrations of the reactants at equilibrium
• Steps to calculate equilibrium constant K

  1. Write the balanced chemical equation

  2. Write the equilibrium expression using the law of mass action

  3. Plug in the equilibrium concentrations/partial pressures
• Relationship between Kc and Kp

  Kp = Kc * (RT)^(Δn)

  Where Δn = Σ(coefficients of products) - Σ(coefficients of reactants)
• The equilibrium constant K is used to determine the position of equilibrium and the extent of a reaction
• j and k


  Coefficients of the reactants
• l and m


  Coefficients of the products
• Delta n


  Sum of the coefficients of the products minus the coefficients of the reactants
• In part a, we are given Kc and want to find Kp
• Delta n for the given reaction is -2
• In part b, we are given Kp and want to find Kc
• Delta n for the given reaction is still -2
• When the coefficients of a reaction are doubled

  The new K value is the original K value squared
• When the coefficients of a reaction are divided by a factor

  The new K value is the original K raised to that factor
• When the reaction is reversed


  The new K value is 1 over the original K value
• 20 moles of NOCl is placed in a 4 L container at equilibrium, 8 moles of Cl2 was found
• Calculating Kc


  1. Write an ICE table

  2. Find equilibrium concentrations

  3. Kc = [NO]^2 * [Cl2] / [NOCl]^2
• Given: [O2] = 0.10 M, [CO2] = 0.75 M at equilibrium, find [CO]
• Ammonia partially decomposes into N2 and H2
• Calculating equilibrium partial pressures

  1. Write an ICE table

  2. Use given H2 partial pressure to solve for x

  3. Calculate NH3 partial pressure at equilibrium