Reaction rates and Equilibrium

• Why does increased concentration increase rate of reaction?

  More likely for particles with high enough Ea to have successful collisions per second, resulting in higher likelihood of reaction occurring
• Why does increased surface area increase rate of reaction?

  Increasing surface area increases the likelihood of successful collisions per second, which increases likelihood of reaction occurring
• Why does increased temperature increase rate of reaction?

  The particles will have increased kinetic energy, therefore more particles will have the required activation energy
• Why does increased pressure increase rate of reaction? ONLY FOR GASES

  The particles will be in a smaller volume, therefore more successful collisions with the necessary Ea will occur, therefore reaction rate will be increased
• What is a catalyst?

  Increases reaction rate without being used up by offering alternative route with lower activation energy
• Why is a catalyst used?

  -To provide a pathway with lower activation energy or provide a surface for the reactant to take place on
• What is a homogenous catalyst?

  A catalyst in the same phase as the reactants
• What is a heterogenous catalyst?

  A catalyst in a different phase as the reactants
• What is beneficial about using a catalyst?

  It reduces temperature required to start non-spontaneous reactions

  -More economically viable than increasing temp/ pressure which uses more fuel
• Maxwell-Boltzmann distribution


  Shows the distribution of energies that molecules of gas or liquid have at a particular temperature

  
• Features of a Maxwell-Boltzmann distribution

  - No molecules have zero energy - the curve starts at the origin

  - The area under the curve is equal to the total number of molecules

  - There is no maximum energy for a molecule - the curve does not meet the x-axis at high energy
• How does Boltzmann distribution change with temperature?

  Higher temperature - Probable speed point shifts right and lower down as more particles are more likely to have Ea
• How does Boltzmann distribution change with catalysts?

  Graph itself does not change - Activation energy
• What is dynamic equilibrium?

  Where the rate of the forward reaction and the rate of the backward reaction are equal in a closed system
• What is important about the concentration of reactants and products in a closed system?

  They do not change
• What is Le Chatelier's principle?

  When changes are made to a system, the system will oppose them
• What happens when temperature is increased in a closed system?

  The reaction will shift in the endothermic direction
• What happens when pressure is increased in a closed system?

  The side with less moles is favoured
• What happens when concentration of product is increased?

  The reactant is favoured
• How do catalysts act in dynamic equilibria?

  They increase the rate of reaction of both the forward and backward reaction equally, resulting in an unchanged position of equilibrium
• What are compromise conditions?

  Conditions that maximise yield of product with the most economically viable conditions
• What is Kc?

  The equilibrium constant
• Kc = 1


  Equilibrium is in the middle
• Kc < 1

  Equilibrium shifts left
• Kc > 1

  Equilibrium shifts right
• How is Kc calculated?

  Kc=[C]^c x [D]^d/[A]^a x [B]^b
• What is the energy rate rule?

  Every 10 degree increase, the rate doubles