Unit 8: Equilibrium

Content Outline: Working with Gaseous Reactions and KP (8.4)

  1. Dynamic Equilibrium (“Dynamic” means “constant movement”; “equilibrium” means “state of being equal”)
  1. This is a “state” where opposite reactions/processes are occurring at the same rate and at the same time in the same space.
  2. Equilibrium is affected by changes in concentrations, pressure, and temperature.
  1. These changes will cause the re-established equilibrium to favor the reactants or products.
  1. Equilibrium in ALL GASES reactions
  1. As all the reactants and products are gases, and most likely contained in reaction vessels, the reaction must abide by the gas laws you studied in Unit 5 (States of Matter).
  1. The most important of the laws being the Ideal Gas Law:

The mathematical equation is:

PV = nRT

R is the Ideal Gas Constant – its value is (0.0821 L*Atm/Mol* K)

V is volume – It is measured in Liters.

T is Temperature – It is measured in Kelvins

P is pressure – It is measured in Atmospheres

n is amount of a substance measured in moles

  1. The Equilibrium Constant (K) is:
  1. K = [Products]

[Reactants]

  1. So combining the two we get the Gas Pressure Constant (KP)
  1. This is done because gases can either be referred to as quantities of pressure (Atm) or in concentrations (mol/L). We must have a way to include both quantities.
  2. KP = KC(RT)Δn

KP= Gas Pressure Constant for a gaseous reaction

KC =Equilibrium Constant

R = Ideal Gas Constant– its value is (0.0821 L*Atm/Mol* K)

T = Temperature in Kelvins (273 + OC)

Δn= Change in number of moles from reactant to products, ONLY gases.

  1. You find by subtraction: # of moles in products – # moles in reactants.
  1. Can be a positive number - # moles of product aregreater than moles of reactants.
  2. Can be a negative number - # moles of products areless than moles of reactants.
  3. If Δn equals zero, then we just say that KP=KC
  • This is because any entity that is raised to the zero power = 1 so… (RT)0 = 1

This is VERY important to remember when calculating.

  1. Using the RICE table method when perform K calculations
  1. This method can be used for performing most K (equilibrium Constant) calculations.
  1. This include: K, KP, KA, KB, and KSP
  2. R = The balanced reaction. This is always your starting point.
  1. Remember, pure substances and water are not included in the calculation, but can be in the equation.
  2. The two equations to be used are:

K = [Products] OR KP = KC(RT)Δn

[reactants]

  1. I = The Initial concentrations
  1. For the products side, this is usually zero.
  2. For unknowns, you use variables such as x (x, x2, x3, or x, 2x, 3x) Just like in your algebra class.
  1. C = Change- This is the change between the initial and final.

a. Pay attention to your exponents here, as exponents of 4 or greater are very minimal and can usually be considered zero change.

  1. E = Equilibrium values

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