Reaction Rates

• What is the equation used to calculate rate?

  Rate = change in concentration / time
• What is the unit for rate of reaction?

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

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

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

  • Temperature
  • Pressure
  • Concentration
  • Surface area
  • Catalyst
• What is the effect of increasing temperature on the rate of reaction?

  Increased temperature leads to increased rate
• Why does increasing temperature increase the rate of reaction?

  More particles have energy greater than activation energy
• What is the effect of increasing concentration/pressure on the rate of reaction?

  Increased concentration/pressure leads to increased rate
• Why does increasing concentration/pressure increase the rate of reaction?

  More particles in a given volume lead to more collisions
• What are the variables that can be monitored to calculate the rate of reaction?

  • Concentration of reactant or product
  • Gas volume of products
  • Mass of substances formed
• How to calculate rate from a concentration-time graph?

  Draw a tangent and find the gradient
• What is a catalyst?

  A substance that increases reaction rate
• How do catalysts work to increase the rate of reaction?

  They provide an alternate pathway with lower activation energy
• What does homogeneous catalyst mean?

  A catalyst in the same phase as reactants
• What does heterogeneous catalyst mean?

  A catalyst in a different phase than reactants
• What are catalytic converters?

  Devices in vehicles to reduce toxic emissions
• Define activation energy.

  The minimum energy for a reaction to occur
• Name some important features of Boltzmann distribution.

  • Area under the curve = total number of molecules
  • Area under the curve does not change with conditions
  • Curve starts at the origin
  • Curve does not touch or cross the energy axis
  • Only molecules with energy > activation energy can react
• What are the axes in a Boltzmann distribution?

  X axis - energy, Y axis - number of molecules

  
• How does increasing temperature affect the Boltzmann distribution curve?

  • Shifts the curve to the right
  • Increases the area under the curve
  • More molecules exceed activation energy
• How does a catalyst affect the Boltzmann distribution curve?

  • Lowers the activation energy
  • Increases the number of molecules exceeding activation energy
  • Shifts the curve to the right