1.5 kinetics

• what is the collision theory?

  for a reaction to take place between two particles, they must collide with enough energy to break bonds
• for a reaction to take place, orientation plays a part as collisions have to take place between the parts of the molecule that are going to react
• what is activation energy

  the minimum amount of energy for collisions to result in a reaction and start breaking bonds
• in a reaction profile, the species that exists at the top of the curve is called a transition state or activated complex
• a transition state is when some bonds are in the process of being made or some are in the process of being broken
• The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of a gas or liquid have at a particular temperature
• what are two factors that effect whether collisions are successful or not?

  kinetic energy and orientation
• what are two factors that effect rate of reaction?

  proportion of collisions that are successful and frequency of collisions
• 5 factors that effect rate of reaction

  1. temperature
  2. concentration
  3. pressure
  4. surface area
  5. catalyst
• most probable energy Emp is the energy that a randomly selected particle is most likely to have
• mean energy = energy levels of all the particle / total number of particle
• hetergeneous catalysts are when catalysts are in different phases to the reactant
• homogeneous catalysts are when catalysts are in the same phase as the reactant
• effect of a catalyst

  A) no catalyst

  B) catalyst

  
• draw an exothermic reaction profile with labels?

  Sure! Here is a simple exothermic reaction profile with labels: 1. Reactants 2. Activation energy 3. Transition state 4. Products 5. Energy released

  A) reactants

  B) products

  C) energy change

  D) activation energy

  
• draw an endothermic reaction profile?

  Endothermic

  
• draw and label the maxwell boltzmann graph (8)

  maxwell boltzmann graph

  A) Emp

  B) activation energy

  
• how can a reaction go into completion most particles have less energy than the activation energy?


  particles gain energy through collisions
• draw two maxwell boltzmann graphs at a higher temperature and lower temperature

  maxwell boltzmann graphs

  
• what shifts in the graph when temperature increases

  the Emp and mean shifts to higher values although the number of molecules with those energy decreases
• what happens to the range of energy when temperature increases?

  increases
• what does the area of a curve tell you?

  the total number of particles
• how do we measure the reaction rate?

  change in concentration / time
• what is the unit for rate of reaction?

  moldm-3 s-1
• what does the gradient of the curve tell you?

  rate of reaction
• • how do you calculate the rate of reaction with sodiumthiosulfate and hydrochloric acid
  • why is this an approximation?
  • why can we use it ?

  1. 1/time
  2. because we dont use concentration
  3. because we assume the amount of sulfur produced is constant and fixed
• what is the effect on increasing concentration and pressure?

  at higher concentration or pressure there are more particles per unit volume so there are more frequent successful collisions
• draw the graph when the concentration/ pressure increases?

  increase

  
• what would a reaction profile look like with a catalyst?

  Lower

  
• what would a maxwell boltsmann graph look like with a catalyst?

  Shifted

  
• what is the effect of increasing temperature refer to activation energy?

  more particles will have more energy greater than activation energy so more successful collisions will occur
• what is the effect in increasing surface area?

  Increased reaction rate as there are more frequent succesful collisions
• what is the effect of a catalyst?

  • lowers activation energy
  • so more particles will have more energy than activation energy
  • so more succesful frequent collisions
  • the reaction will be faster
• what is a catalyst?

  a substance that lowers activation energy by providing an alternative pathway without being used up
• different ways of calculating rate?


  1. disappearing cross experiment
  2. gas syringe