Kinetics 3.4

• What is the definition of Activation Energy (AE)?

  Reactant particles collide with enough energy and correct orientation
• How is the Rate of Reaction (ROR) defined?

  Measure of the amount of reactants used up or products formed in a given period of time
• What does the Maxwell-Boltzmann Distribution illustrate?

  It shows how kinetic energy of molecules in gas/liquid are distributed at a certain temperature (T)
• What is a catalyst?


  Finely divided rare metals that speed up the rate of reaction without being used up
• What are the factors affecting the Rate of Reaction according to Collision Theory?

  • Temperature
  • Pressure/Concentration
  • Surface Area (SA)
  • Catalyst
• How does an increase in temperature affect the Rate of Reaction?

  Particles have greater/equal energy to AE, move quicker, and have more frequent/successful collisions
• How does pressure or concentration affect the Rate of Reaction?


  More particles lead to a greater chance of collision, increasing the number of successful collisions in a given period of time

  
• What is the effect of increasing surface area on the Rate of Reaction?

  Increasing surface area decreases particle size, leading to more collisions and successful collisions in a given period of time

  
• How does a catalyst increase the Rate of Reaction?

  A catalyst provides an alternative pathway with lower activation energy, allowing more particles to have enough energy to collide successfully

  
• What is the chemical reaction for measuring the volume of gas produced with HCl and Mg?

  HCl + Mg → MgCl2 + H2
• What happens to the magnesium in the reaction with HCl?


  Mg disappears as it reacts
• What is observed when the reaction with HCl and Mg is complete?


  Bubbles stop and the syringe stops moving
• How does increasing temperature affect the graph of Rate of Reaction?


  Higher temperatures result in more energy, more successful collisions, a faster Rate of Reaction, and a steeper graph at the start

  
• What are the key features of the Maxwell-Boltzmann Distribution?

  • Begins at (0,0) since no particles have 0 energy
  • Curve never meets x-axis as there are never 0 particles
  • Area under the curve to the right of AE line represents particles with energies greater/equal to AE
  • Higher temperatures increase the number of particles with energies equal/greater than AE

  
• What happens to the area under the Maxwell-Boltzmann Distribution graph when temperature increases?


  The total area remains the same, but the peak moves right and down slightly
• How does adding a catalyst affect the activation energy?


  It lowers the activation energy so more particles have enough energy to collide successfully
• What is chemisorption in catalysis?


  Molecules are adsorbed on the surface through interactions of d orbitals of the metal in a favorable orientation for reaction
• What happens to bonds during chemisorption in catalysis?


  Bonds are weakened or broken completely
• What is the role of a catalyst in a catalytic converter?


  It helps to convert toxic gases into less toxic gases
• Why is it important to get the right amount of oxygen in the fuel-air mixture in a catalytic converter?


  Otherwise, the catalytic converter will not work efficiently
• What happens to the gases leaving the catalytic converter?


  They are much less toxic than those entering it
• What is the problem with using leaded petrol in a catalytic converter?


  Leaded petrol deposits lead on the catalyst's surface, blocking active sites and "poisoning" it
• What is a heterogeneous catalyst?


  • A catalyst in a different physical state to the reactants and products
  • Favored in industry for easy separation from products
  • Often less specific and allows side reactions to occur
• What are the economic benefits of using catalysts in industrial reactions?


  • Speed up reactions that may be too slow to be feasible or profitable
  • Reduce the need for high pressures and temperatures, making processes more economically viable
• What catalysts are used in the following industrial processes?

  • Making ammonia (Haber Process): Iron
  • Making sulfuric acid (Contact Process): Vanadium(V) oxide
  • Making nitric acid (Ostwald Process): Platinum and rhodium alloy
• Exothermic diagrams have higher reactants than products
• This is an Endothermic diagram

  
• Endothermic diagrams have higher products than reactants
• This is an Exothermic diagram

  
• How do gaseous products affect pressure/concentration


  They increase pressure and brings particles closer together, increasing rate of reaction
• What are the 2 ways to measure ROR

  Measuring: Volume of gas produced/Loss in mass of reaction
• Why does a higher temperature lead to more successful collisions in a chemical reaction?

  Higher temperatures provide more energy to the molecules, increasing their movement.

  
• How does the graph of a reaction change with higher temperatures?

  The graph becomes steeper at the start, indicating a faster rate of reaction.
• What is the effect of higher temperatures on the time it takes for a reaction to finish?

  The reaction finishes faster at higher temperatures.

  
• What remains the same when only reaction conditions change?

  The volume of gas remains the same.
• Why is the Maxwell-Boltzmann Distribution important?

  Important for understanding reaction rates and temperature effects

  
• How can you tell a catalyst is added in a Maxwell-Boltzmann graph?


  Shown on graph by larger area under graph past AE

  
• How does chemisorption affect the AE?

  Lowers AE
• What happens to the products after the bonds are weakened/broken in chemisorption?

  Products desorb
• What is a gas that leaves the catalytic converter that contributes to global warming?

  CO₂