1.6 Equilibria

• What is dynamic equilibrium? [2]

  A reversible reaction in which the forward and reverse reactions are occurring at the same rate. The concentrations of the reactants and products remain constant (DO NOT SAY THE SAME).
• Why does equilibrium have to be established in a closed container?

  To prevent any products or reactants from escaping.
• What does Le Chatelier's principle state?

  If a change is made to a system at dynamic equilibrium then the position of equilibrium will move to oppose the change.
• What 4 factors can be changed in reactions in equilibrium?

  ○ Pressure.

  ○ Temprature.

  ○ Concentration.

  ○ Catalyst - only speeds up the reaction, does not change the position of equilibrium.
• Is a reaction with an enthalpy change of -9.6kJmol⁻¹ exothermic or endothermic?

  Exothermic as heat is let off
• Is a reaction with an enthalpy change of 9.6kJmol⁻¹ exothermic or endothermic?

  Endothermic as heat is absorbed
• If the enthalpy change of a forward reaction is -9.6kJmol⁻¹ what is the value for the reverse reaction? Is the reverse reaction exothermic or endothermic?

  9.6kJmol⁻¹ and endothermic
• If the forward reaction is exothermic and the temprature is increased will equilibrium shift to the right or left and what effect will this have on the yield of product?

  Equilibrium will shift to the left and the yield of product will decrease.

  
• If the forward reaction is endothermic and the temprature is increased will equilibrium shift to the right or left and what effect will this have on the yield of product?

  Equilibrium will shift to the right and the yield of product will increase.

  
• The yield of product is directly proportional with increasing temprature is this an exothermic or an endothermic reaction?

  It's endothermic as when the temprature increases so does the yield of product.

  
• The higher the number of moles on a side, the higher the pressure
• In the reaction 2SO₂ + O₂ <-> 2SO₃ If the pressure in the system is increased will equilibrium shift to the right or the left? Why?

  Equilibrium will shift to the right to decrease the pressure as there are a lower number of particles on that side.
• In the reaction 2SO₂ + O₂ <-> 2SO₃ If the pressure in the system is decreased will equilibrium shift to the right or the left? Why?

  Equilibrium will shift to the left to increase the pressure as there are a higher number of particles on that side.
• In the reaction 2SO₂ + O₂ <-> 2SO₃ If more oxygen is added will equilibrium shift to the left or right and what effect will this have on the yield of 2SO₃?

  Equilibrium will shift to the right to make more 2SO₃ resulting in less O₂ and a higher yield of product.
• In the reaction 2SO₂ + O₂ <-> 2SO₃ If more 2SO₃ is added will equilibrium shift to the left or right and what effect will this have on the yield of 2SO₃?

  Equilibrium will shift to the left to make more 2SO₂ and O₂ resulting in a lower yield of product.
• In the reaction 2SO₂ + O₂ <-> 2SO₃ If some oxygen is removed will equilibrium shift to the left or right and what effect will this have on the yield of 2SO₃?

  Equilibrium will shift to the left to make more O₂ resulting in a lower yield of product.
• What effect does a catalyst have on the position of equilibrium?

  No effect
• What does a catalyst do in an equilibrium reaction? [2]

  It speeds up BOTH the forward and reverse reactions EQUALLY resulting in equilibrium being established quicker.
• A 70% equilibrium yield of product is obtained at 350°C and 400kPa. Explain why an industrial chemist may choose to operate at 1) a higher temperature and 2) lower pressure than those given

  A higher temprature will increase the rate of reaction. Generating high pressure is expensive.
• For equilibrium reactions what are the two major factors which industries may consider?

  Yield - how much product is obtained.

  Rate - how fast the reaction reaches equilibrium.
• For an industry what might be the two compromises for a high temprature or a low temprature in terms of equilibrium yield.

  A high temprature results in fast rates of reactions however have high energy costs making them expensive.

  A low temprature produces a lower yield and are cheaper but provides slower rates of reaction
• What is an homogeneous system?

  One in which all reactants and products are in the same phase or state.
• What's the equasion for a mole fraction?

  Mole fraction = moles of species / total moles in equilibrium mixture
• aA + bB <-> cC + dD Write the expression for the equilibriu constant (Kc)

  Fill in the blank:

  A) [C]

  B) c

  C) [D]

  D) d

  E) [A]

  F) a

  G) [B]

  H) b

  
• Fill in this table:

  A) Exothermic

  B) Increased

  C) Decreased

  D) Left

  E) Right

  F) Decrease

  G) Increase

  H) Endothermic

  I) Increased

  J) Decreased

  K) Right

  L) Left

  M) Increase

  N) Decrease