Dynamic equilibria

• What is a reversible reaction?


  a reaction where the products can react together to form the original reactants

  - it can go both ways
• What is the haber process?


  Nitrogen and hydrogen react to form ammonia
• What is the equation for the haber process?


  N2 + 3H2 --> 2NH3
• How is the nitrogen obtained?


  From the air = 78% nitrogen
• How is the hydrogen obtained?


  Can be extracted from hydrocarbons from sources such as natural gas and crude oil
• At what levels is the haber process carried out?


  450ºC

  200 atmospheric pressure

  Iron catalyst
• What is dynamic equilibrium?


  The forward and backward reactions are both happening at the same tine and at the same rate and the concentrations of the reactant and products have reached a balance and won't change
• What is an open system?


  Energy and matter can both go in and out
• What is a closed system?


  Where energy can go in and out, but matter cannot do either
• What must happen for a reversible reaction to take place?


  It must happen in a closed system
• What is stage 1 of equilibria?


  Concentration of A+B is at its highest

  Forwards rate is longest

  There is NO C+D = no backwards reaction
• Stage 2?


  Conc of A+B has decreased = rate decreases slightly

  Small conc of C+D = slow backwards rate of reaction
• Stage 3?

  Conc of A+B continues to decreases, as does the forwards rate.

  The conc of C+D continues to increase, speeding up the backwards reaction
• Stage 4?


  The forwards rate = the backwards rate

  Therefore the relative cones of A+B+C+D stop changing
• What is one rule about dynamic equilibrium?


  The rates will be equal, but not always the concentrations
• When does the equilibrium lie to the left?


  When there is morereactantthan products
• When does the equilibrium lie to the right?


  When their is moreproductthan reactants
• When does the equilibrium lie in the middle?


  When their is equal amounts of both product and reactant
• What 3 things can change the position of equilibria?


  Temperature, pressure (for equilibria involving gases) and concentration (of reactant and products)
• What is Le Chatelier's principle?


  If theres achangein temperature, pressure or concentration in a reversible reaction the equilibrium position will move to helpcounteractthat change
• What happens if you decrease temperature?


  The equilibria will move into the exothermic direction = producing more heat
• What happens if you increase temperature?


  Equilibrium will move into the endothermic direction = absorbing more heat
• What does changing the pressure only affect?


  Equilibria involving gases
• What happens if you increase the pressure?


  The equilibrium will move to the side of fewer molecules of gas to reduce pressure.
• What happens if you decrease the pressure?


  The equilibrium will move to the side that has more molecules of gas to increase pressure
• What happens if you increase the concentrations of the reactants?


  The equilibrium will move to the right = to use up the reactants (making more products)
• What happens if you increase the pressure of the products?


  The equilibrium will shift to the left to use up the products (making more reactants)
• What does endothermic mean?


  That the reaction requires heat energy from the surroundings to work
• Why would you use an iron catalyst?


  To increase the rate of reaction
• Why use the temperature 450º?


  It is a compromise between rate of reaction and yield
• Why is 200atm pressure used?


  It is a compromise between rate and yield vs cost