Chapter 10

• What is collision theory?

  For a reaction to occur particles must collide with:

  • correct orientation
  • energy greater than the activation energy
• What factors affect the rate of reaction?

  • temperature
  • concentration (pressure when using gases)
  • use of catalyst
  • surface area of the solid
• What happens when changing concentration?

  lower

  • less particles are in a given volume, causing less frequent collisions and therefore slower rate of reaction

  higher

  • more particles in a given volume, more frequent collisions and therefore faster rate of reaction
• What is a catalyst?

  A substance that increase the rate of chemical reaction without undergoing any permanent change itself:

  • not used up
  • regenerates at the end of a reaction
  • provides an alternative pathway for a reaction with a lower activation energy
• Homogeneous catalyst?

  Has the same physical state as the reactants
• Heterogeneous catalyst?


  Has a different physical state from the reactants

  • the reactant molecules form weak bonds with the catalyst surface - called "adsorbtion"
• What is the process of a catalyst working?

  Bonds form with reactants and catalsyst surface

  Bonds break between reactant molecules

  Bonds form between the two different reactant molecules

  Bonds break between product and catalyst surface (leaving the surface = desorption)
• What is adsorption?


  When the reactant molecules form weak bonds with the catalyst surface
• What are the sustainability benefits of using catalysts?

  Increased rate of chemical reactions - alternative pathway - lower activation energy

  Lowers temperature needed for the reaciton

  Less energy needed - less fossil fuels used up

  Reduction of CO2 emissions (other atm pollutants) -methane, H2O
• What does the Boltzmann distribution curve show?

  The distribution of molecular energies in a sample of gas molecules
• What goes on each axis of the Boltzmann distribution curve?

  X = energy

  Y = number of molecules / particles
• What does the area under the Boltzmann curve show?

  total number of molecules
• What is the affect of temperature on the Boltzmann distribution curve?

  Normal temp = high peak at the start and then fades out

  Increased temp = peak is lower and shifted to the right

  This is because more molecules have energy higher than the activation energy - greater proportion of collisions will lead to a reaction
• Effect of catalyst on curve?

  greater proportion of molecules exceed the new activation energy

  more molecules collide with energy > Ea

  more effective collisions - faster rate of reaction
• What is a closed system?

  Where no particles can enter or exit the system, no changes occur due to changes in the external environment
• What is chemical equilibrium?

  Where both the forward and backward reaction take place at the same rate
• Affect of concentration on equilibrium

  Increase reactants (or decrease products):

  equilibrium shifts to the right

  Decrease reactants (or increase products):

  equilibrium shifts to the left
• Affect of temperature on equilibrium?

  Increase temperature:

  Shifts to the endothermic side

  Decrease temperature:

  Shifts to the exothermic side
• Effect of pressure on equilibrium?

  Increase:

  Shift to side with least moles of gaseous molecules

  Decrease:

  Shift to side with most moles of gaseous molecules
• Effect of catalyst on equilibrium?


  Does NOT change position of equilibrium

  Will increase rate of reaction (that equilibrium has established)

  Speeds up rate of both forward and backward reactions
• Chemical industry evaluation for Ammonia

  Decrease in temp will favour products reaction but slow rate = 350-500

  High pressure favours yield of ammonia but more expensive = 100-200atm

  Remove ammonia as it forms to decrease concentration of products

  Iron catalyst used so reaction can take place at lower temp and pressure
• What is the equation for equilibrium constant


  Kc = (C)c x (D)d / (A)a x (B)b
• What is equilibrium constant?

  Magnitude tells us the relative proprtion of reactant and products in the equilibrium system - tells us which side the equilibrium lies on

  Kc = 1 - lies in the center

  Kc = > - lies on the right (products > reactant)

  Kc = < - lies on the left (products < reactant)