1.5 Kinetics

• rate of reaction definition

  the change in concentration per unit time
• activation energy definition

  the minimum energy required for particles to collide for a reaction to occur
• why can a reaction go to completion even though few particles have energy greater than the activation energy?

  particles gain energy through collisions
• what does the Maxwell-Boltzmann graph show?

  the spread of energies that molecules have
• why does the Maxwell-Boltzmann curve go through the origin?

  there are no molecules with zero energy
• increasing surface area results in more frequent, successful collisions between particles which increases the rate of reaction.
• A catalyst increases the rate without being used up by providing an alternate pathway with lower activation energy.
• increasing temperature means there are more molecules with energy greater than the activation energy so there are more frequent, successful collisions which increases rate of reaction.
• The red curve shows an increase in temperature.

  A) original curve

  
• increasing concentration and pressure means there are more particles in a given volume, so more molecules have energy>Ea, which results in more frequent and successful collisions, therefore increasing the reaction rate.
• Comparing Rate Curves: if the temp/conc/surface area is higher, the curve has a steeper gradient. Different volumes of same conc means the curves have same initial rate but end at different points.
• a small increase in temperature can lead to a large increase in rate as there are more collisions which have more energy
• experiment 1:

  • place a piece of paper marked with a cross under the reaction beaker
  • time how long it takes for the cross to disappear
  • PROBLEM - difficult to know when exactly the cross disappears
  • use the same observer to reduce this error
• experiment 2:

  • place reaction on mass balance
  • measure the change in mass as gas is lost
  • use a fume cupboard if the gas is toxic or harmful
• experiment 3:

  • use a gas syringe to measure the amount of gas produced over a specified time