The chatelier's principle

• Le Châtelier's Principle states that if a system at equilibrium is disturbed by a change in pressure, temperature, or concentration of reactants or products, the system will shift its position to counteract the effect of the disturbance and restore equilibrium.
• , if you increase the concentration of a reactant in a system at equilibrium, the system will shift to the right to use up some of the added reactant and restore equilibrium. If you decrease the pressure by increasing the volume of the system, the system will shift in the direction that produces more moles of gas to counteract the decrease in pressure.
• When any system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established.
• Increasing the amount of one reactant causes the reaction to go further in the opposite direction so as to consume more of this excess reactant.
• When the forward and reverse reaction occur at the same rate, the reaction is said to be in ___________

  equilibrium
• Le Chatelier's principle states that


  if a system at equilibrium is disturbed, the equilibrium position will shift to counter the effects of the disturbance
• What happens to the equilibrium if a reactant's concentration is increased?

  Favors the forward reaction
• What happens to the equilibrium if a reactant's concentration is decreased?

  Favors the reverse reaction
• What happens to the equilibrium of an exothermic rxn if heat is added? Why?

  The reverse rxn is favored because heat is a product.
• What happens to the equilibrium of an endothermic rxn if heat is added?

  The forward rxn is favored because heat is a reactant.
• For the rxn A + B <−> C + D, what happens if C or D are reduced?

  Forward rxn is favored
• For the rxn: 2A (g) + 3B (g) <−> C (g) + 3D, what happens if pressure is reduced?

  The reverse rxn is favored because the equilibrium shifts toward the larger moles of gas which are on the left side.
• How does the equilibrium change if a catalyst is added?

  No change in equilibrium (catalysts only change rate at which equilibrium is reached)
• When you take something away from a system at equilibrium the system shifts in such a way as to _________ some of what you've taken away

  replace
• When you add something to a sys at equilibrium the system shifts in such way as to _______ some of what you've added

  use up
• Define Le Chatelier's principle

  any change in a system at equilibrium results in a shift of equilibrium in direction which minimizes (opposes) change. "dynamic equilibrium concept"
• Define dynamic equilibrium

  When the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations of reactants and products remain unchanged.
• Define position of equilibrium

  The ratio of the concentration of products to reactants
• Consider the following exothermic reaction in equilibrium:

  4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g)

  State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if water is removed.

  The [HCl] ↓ and [Cl]↑ as system moves to right to oppose removal of water
• Consider the following exothermic reaction in equilibrium:

  4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g)

  State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if the temperature of the container was increased.

  The [HCl] ↑ and [Cl]↓ as system moves to left to oppose increase in temperature and moves in endothermic direction.
• Consider the following exothermic reaction in equilibrium:

  4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g)

  State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if a catalyst is introduced.

  NO CHANGE in [HCl] or [Cl] as a catalyst speeds up the rate of both the forward and backward reaction.
• State whether a high or low temperature and a high or low pressure should be used to maximize the yield of product:

  2SO₂(g) + O₂(g) ↔ 2SO₃(g), ∆H = -kJ (exo)

  Low temperature (Opposes decrease by moving in exdothermic direction)

  High pressure (Opposes increase by moving to side with least moles)
• Q. The Haber process involves an equilibrium reaction:

  N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ

  The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst.

  Give one reason why a higher temperature is not used.

  System would oppose change move backwards in endothermic direction and yield of NH₃ would decrease.
• Q. The Haber process involves an equilibrium reaction:

  N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ

  The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst. Give two reasons why a lower pressure is not used

  System would oppose change move backwards in favor of more moles and yield of NH₃ would decrease. Collision frequency would decrease so rate decreases.
• Q. The Haber process involves an equilibrium reaction:

  N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ

  The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst. Why is a catalyst used?

  To lower the actiavtion energy and speed up the reaction.See an expert-written answer!We have an expert-written solution to this problem!
• CO₂(aq) ↔ CO₂ (g) ∆H = -kJ (exo) Use Le Chatelier's principle to explain what happens to the CO₂ concentration in water when a can of soft drink is shaken up and then opened.


  The system is no longer just the bottle but the universe. The [CO₂] in the universe is much lower so the system will move to the right to oppose the change. Dissolved CO₂decreases and so the drink goes 'flat'.
• CO₂(aq) ↔ CO₂ (g) ∆H = +KJ (endo) Use Le Chatelier's principle to explain why is it important to serve "fizzy" drinks chilled rather than warm?

  If fizzy drink gets warm the system will oppose the change by moving in the enothermic direction. Less CO₂is dissolved and drink will go flat.See an expert-written answer!We have an expert-written solution to this problem!
• increasing concentration of reactants causes___________

  shift right (forward)
• increasing concentration of products causes_________

  shift left (reverse)
• decreasing volume causes __________

  shifts towards fewer moles of gas particles
• increasing volume causes __________

  shift towards greater moles of gas particles
• exothermic: increasing temperature causes ________

  shift left (reverse)
• exothermic: decreasing temperature causes __________

  shift right (forward)
• endothermic: increasing temperature causes __________

  shift right (forward)
• endothermic: decreasing temperature causes __________

  shift left (reverse)
• Is equilibrium static or dynamic?

  Dynamic: the reaction keeps going in the forward and reverse directions
• states that changing a factor such as concentration, temperature, or pressure of a rxn at equilibrium will cause the reaction to shift in the direction that counteracts the effect of that change

  Le Chatelier's Principle
• occurs when the rate of the forward rxn is equal to the rate of the reverse rxn

  Chemical Equlibrium
• increase the rate of rxn by decreasing its activation energy, has no effect on equilibrium concentrations.

  Catalyst
• an explanation of the variability in reaction rates that is based on the idea that molecules must collide in order to react

  Collision Theory