Chemical Equilibrium

• Reversible reactions


  Chemical reactions that can proceed in either direction
• Chemical equilibrium / Dynamic equilibrium


  • The state in a chemical reaction wherein the concentrations of the reactants and products remain constant
  • The rates of the forward and reverse reaction are the same
• Haber process

  Enables the commercial production of ammonia from combining nitrogen gas with hydrogen gas
• Equilibrium constant (Kc)

  • In 1864 two Norwegian scientists named Cato Gulberg (1836 - 1902) and Peter Waage (1833 - 1900) proposed the law of mass action to explain why chemical equilibrium occurs
• Factors that may influence chemical equilibrium

  • Concentration
  • Temperature
  • Pressure
• Chemical equilibrium may shift in favor of either the reactants or the products depending on certain factors
• Decrease in temperature


  Equilibrium shifts to the left, reactant formation is favored
• Equilibrium constant (Kc) = 1


  Products and reactants are in equilibrium
• Heterogeneous equilibria


  In which the participating chemical components are present in more than one phase
• Calculations involving equilibrium


  1. Write the balanced equation

  2. Write the equilibrium expression

  3. Prepare a table showing the initial molar concentrations

  4. Set up representations for the changes in the molar concentrations

  5. Define the equilibrium concentration by applying the change to the initial molar concentration

  6. Apply those equilibrium concentrations to the equilibrium expression
• Le Chatelier's Principle


  If stress is applied on a system at equilibrium, then the equilibrium will shift to the direction where the stress will be relieved
• Increase in pressure for a gas-phase reaction


  Equilibrium shifts toward the side with fewer number of gaseous molecules
• Increase in pressure


  Does not affect the magnitude of Kc but the concentration of each chemical substance will have to change in response to the increase in pressure
• Magnitude (Kc)


  describes the extent to which the reaction favours either the forward reaction or the reverse reaction at equilibrium
• If Kc is very large, equal to or greater than 1000, and the equilibrium shifts to the right, the reaction favors a forward reaction
• when the backward reaction is favored Kc has small Values, that are equal to or less than 1000. The equilibrium position shifts to the left
• Q<Kc


  the equilibrium shifts to the RIGHT. PRODUCT formation is favored
• Q>Kc


  The equilibrium shifts to the LEFT. REACTANT formation is favored
• Q=Kc

  The system is at EQUILIBRIUM. NO shift in the direction of the equilibrium position