Kinetics

• What is the activation energy (EA)?

  Minimum energy needed for a reaction
• What does the Maxwell-Boltzmann energy distribution illustrate?

  Spread of energies in gas or liquid
• Why does the energy distribution curve go through the origin?

  There are no molecules with no energy
• Why should the energy distribution curve never meet the x-axis?

  No maximum energy for molecules exists
• Where is the mean energy of particles located on the curve?

  Not at the peak of the curve
• What does the area under the Maxwell-Boltzmann curve represent?

  Total number of particles present
• Why do a few particles have low energies?

  Collisions cause some particles to slow down
• How many particles have energy greater than the activation energy?

  Only a few particles have that energy
• What happens to the energy distribution as temperature increases?

  More molecules have higher energies
• What remains constant as temperature increases in the energy distribution?

  Total area under the curve remains constant
• How does the range of energies change with temperature?

  Wider range of energies at higher temperatures
• What happens to the Emp and mean energy at higher temperatures?

  Both shift to higher energy values
• What is required for reactions to occur?

  Collisions with sufficient energy
• What is the usual unit for measuring reaction rates?

  mol dm^-3s^-1
• How is the rate of reaction determined from a concentration vs. time graph?

  Gradient of the curve indicates the rate
• What is the initial rate of reaction?

  Rate at the start of the reaction
• How can reaction rates be calculated from graphs?

  By drawing a tangent and calculating the gradient
• What effect does increasing concentration have on reaction rates?

  Higher frequency of effective collisions
• How does the shape of the energy distribution curve change with increased concentration?

  Curves are higher, area under increases
• What happens to the number of molecules with energy > EA when concentration increases?

  More molecules have energy > EA
• How do different volumes of the same initial concentrations affect initial rates?

  Same initial rate but different final amounts
• What factors increase the rate of reaction?

  Higher concentration, temperature, surface area
• How is the reaction rate measured in the sodium thiosulfate and hydrochloric acid experiment?

  As 1/time for cross disappearance
• Why is measuring 1/time an approximation for reaction rate?

  It does not include concentration
• What happens to the frequency of effective collisions with increased surface area?

  Successful collisions occur more frequently
• What is the definition of a catalyst?

  Increases reaction rates without being used
• How do catalysts affect activation energy?

  Provide an alternative route with lower EA
• What is the effect of lower activation energy on reaction rates?

  Higher frequency of effective collisions
• How does increasing temperature affect particle collisions?

  Increases frequency and energy of collisions
• What happens to the proportion of particles with energy > EA at higher temperatures?

  Significantly larger proportion exceeds EA
• What are the effects of increasing concentration and pressure on reaction rates?

  • More particles per unit volume
  • Greater frequency of effective collisions
  • Energy distribution curves remain unchanged
  • Area under the curves increases
• What are the effects of increasing surface area on reaction rates?

  • More frequent successful collisions
  • Increases the rate of reaction
• What are the effects of catalysts on reaction rates?

  • Increase reaction rates
  • Provide an alternative route with lower activation energy
  • Do not get used up in the reaction
• What are the effects of increasing temperature on reaction rates?

  • Increases energy of particles
  • More frequent collisions
  • More particles exceed activation energy
• How does the activation energy differ between catalyzed and uncatalyzed reactions?

  • Catalyzed reactions have lower activation energy
  • More particles exceed activation energy in catalyzed reactions
• What is the relationship between reaction rate and concentration?

  • Higher concentration leads to faster reaction rates
  • Doubling concentration doubles the number of particles per unit volume
• What is the relationship between reaction rate and temperature?

  • Higher temperature leads to faster reaction rates
  • More particles have energy greater than activation energy
• What is the relationship between reaction rate and surface area?

  • Increasing surface area increases reaction rates
  • More frequent successful collisions occur
• How do you measure reaction rates in experiments?

  • Measure change in concentration over time
  • Use graphs to determine the gradient
• What is the significance of the area under the Maxwell-Boltzmann curve?

  • Represents total number of particles present
  • Important for understanding reaction dynamics