Mr. Strickland's Chemistry     pi-sigma

Topic 6: Chemical Kinetics

 

6.1 Collision theory and rates of reaction

Essential idea: The greater the probability that molecules will collide with sufficient energy and proper orientation, the higher the rate of reaction.

Understandings:

  • Species react as a result of collisions of sufficient energy and proper orientation.
  • The rate of reaction is expressed as the change in concentration of a particular reactant/product per unit time.
  • Concentration changes in a reaction can be followed indirectly by monitoring changes in mass, volume, and colour.
  • Activation energy (Ea) is the minimum energy that colliding molecules need in order to have successful collisions leading to a reaction.
  • By decreasing Ea, a catalyst increases the rate of a chemical reaction without itself being permanently chemically changed.

 

Applications & Skills:

  • Description of the kinetic energy in terms of the movement of particles whose average kinetic energy is proportional to temperature in kelvin.
  • Analysis of graphical and numerical data from rate experiments.
  • Explanation of the effects of temperature, pressure/concentration, and particle size on rate of reaction.
  • Construction of Maxwell-Boltzmann energy distribution curves to account for the probability of successful collisions and factors affecting these, including the the effect of a catalyst.
  • Investigation of rates of reaction experimentally and evaluation of the results.
  • Sketching and explanation of energy profiles with and without catalysts.

 

Guidance:

  • Calculation of reaction rates from tangents of graphs of concentration, volume or mass vs time should be covered.
  • Students should be familiar with the interpretation of graphs of changes in concentration, volume or mass against time.

 

International-mindedness:

  • Depletion of stratospheric ozone has been caused largely by the catalytic action of CFCs and is a particular concern in the polar regions. These chemicals are released from a variety of regions and sources, so international action and cooperation have been needed to ameliorate the ozone depletion problem.

 

Theory of knowledge:

  • The Kelvin scale of temperature gives a natural measure of the kinetic energy of gas whereas the artificial Celsius scale is based on the properties of water. Are physical properties such as temperature invented or discovered?