Topic 9: Kinetics 1

• What is the equation used to calculate rate?

  Change in concentration / time
• What is the unit for rate of reaction?

  mol/dm -3 s-1
• What must particles do in order to react?

  Collide with sufficient energy (activation energy) and the correct orientation
• Do most collisions result in a reaction?

  No.
• What are the factors that affect rate of reaction?

  Temperature, concentration, surface area, catalysts, pressure
• What is the effect on increasing temperature on rate of reaction and why?

  Increase.

  Much higher proportion of particles have energy greater than the activation energy, meaning more successful collisions per second
• What is the effect of increasing pressure/ concentration on rate of reaction and why?

  Increase.

  Concentration= There are more particles in a given volume, meaning more frequent collisions

  Pressure= Molecules are packed closer together into a smaller volume
• What variables can be monitored in an experiment to calculate rate of reaction?

  • Concentration of reactant/ product
  • Gas volume of products
  • Mass of substances formed
• What is a catalyst?

  A substance that increases rate of reaction without being used up.
• How do catalysts work and how do they increase rate of reaction?

  • They provide an alternative reaction pathway with a lower activation energy
  • Activation energy is lower= more particles have the energy to react, so more frequent collisions
• What is a homogenous catalyst?

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

  A catalyst that is in a different phase from the reactants.

  e.g. gaseous reactants passed over solid catalyst
• What are the economical benefits of using catalysts in industrial processes?

  Catalysed reactions happen at a lower temperature so less fuel is needed, meaning fewer emissions from fuels.

  Catalysed reaction enables use of an alternative process with higher atom economy so fewer raw materials are needed and less waste products are produced
• Define activation energy

  Minimum amount of energy that particles must collide with in order to react
• Name some important features of Boltzmann Distribution

  • Area under the curve=total number of molecules
  • Area under the curve doesn't change when conditions alter
  • The curve starts at the origin
  • Curve does not touch or cross energy axis
  • Only molecules with energy greater than the activation energy can react
• What are the axis in Boltzmann distribution?

  X- energy

  y- number of molecules with a given energy
• What happens to the Boltzmann distribution curve at increases temperature?

  Shifts to the right
• What happens to the Maxwell- Boltzmann distribution curve when concentration and pressure are increased?

  • Does not shift
  • Increasing concentration and pressure makes successful collisions happen more frequently but DOESN'T change the energy of the individual particles
• What is the effect of increasing the surface area on rate of reaction?

  Increase

  There is a higher number of exposed reactant particles, so there are more frequent successful collisions.
• What happens to the distribution curve when surface area is increased?

  . Doesn't change

  . It doesn't change the energy of the individual particles, it just increases collisions
• What happens to the distribution curve when a catalyst is used?

  Shifts to the left.

  A greater proportion of molecules have sufficient energy to react as a lower activation energy is required.
• Why do transition metals make good catalysts?

  They have variable oxidation states.

  Electrons are transferred to produce a reactive intermediate and speed up the reaction rate,
• How does a solid catalyst work?

  • Adsorbs molecules onto an active site on the surface of the catalyst
  • Active sites increase the proximity of the molecules and weaken the covalent bonds in the molecules
  • Reactions occur more easily and the rate is increased