collision theory

Examples of collision theory in the following topics:

• The Collision Theory

  • Collision Theory provides a qualitative explanation of chemical reactions and the rates at which they occur.
  • A basic principal of collision theory is that, in order to react, molecules must collide.
  • In fact, the collision theory says that not every collision is successful, even if molecules are moving with enough energy.
  • According to the collision theory, the following criteria must be met in order for a chemical reaction to occur:
  • Discuss the role of activation energy, collisions, and molecular orientation in collision theory

• Transition State Theory

  • TST is used to describe how a chemical reaction occurs, and it is based upon collision theory.
  • TST is also referred to as "activated-complex theory," "absolute-rate theory," and "theory of absolute reaction rates."
  • This third postulate acts as a kind of qualifier for something we have already explored in our discussion on collision theory.
  • According to collision theory, a successful collision is one in which molecules collide with enough energy and with proper orientation, so that reaction will occur.
  • However, according to transition state theory, a successful collision will not necessarily lead to product formation, but only to the formation of the activated complex.

• Heterogeneous Catalysis

  • The reason such catalysts are able to speed up a reaction has to do with collision theory.
  • Recall that according to collision theory, reactant molecules must collide with proper orientation.

• Changes in Concentration

  • This observation is supported by the collision theory.
  • As the concentration of CO is increased, the frequency of successful collisions of that reactant would increase also, allowing for an increased forward reaction—increased generation of product.

• Le Chatelier's Principle

  • This observation is supported by the collision theory.
  • As the concentration of CO is increased, the frequency of successful collisions of that reactant would increase as well, allowing for an increase in the forward reaction, and thus the generation of the product.

• Kinetic Molecular Theory and Gas Laws

  • The following are the basic assumptions of the Kinetic Molecular Theory:
  • The collisions exhibited by gas particles are completely elastic; when two molecules collide, total kinetic energy is conserved.
  • If the reaction is kept at constant pressure, they must stay farther apart, and an increase in volume will compensate for the increase in particle collision with the surface of the container.
  • Reviews kinetic energy and phases of matter, and explains the kinetic-molecular theory of gases.
  • Express the five basic assumptions of the Kinetic Molecular Theory of Gases.

• Distribution of Molecular Speeds and Collision Frequency

  • According to the Kinetic Molecular Theory, all gaseous particles are in constant random motion at temperatures above absolute zero.
  • The movement of gaseous particles is characterized by straight-line trajectories interrupted by collisions with other particles or with a physical boundary.
  • Depending on the nature of the particles' relative kinetic energies, a collision causes a transfer of kinetic energy as well as a change in direction.
  • In theory, this energy can be distributed among the gaseous particles in many ways, and the distribution constantly changes as the particles collide with each other and with their boundaries.
  • Although higher velocity states are favored statistically, however, lower energy states are more likely to be occupied because of the limited kinetic energy available to a particle; a collision may result in a particle with greater kinetic energy, so it must also result in a particle with less kinetic energy than before.

• Gas Diffusion and Effusion

  • The kinetic theory describes a gas as a large number of submicroscopic particles (atoms or molecules), all of which are in constant rapid motion that has randomness arising from their many collisions with each other and with the walls of the container.
  • For effusion to occur, the hole's diameter must be smaller than the molecules' mean free path (the average distance that a gas particle travels between successive collisions with other gas particles).
  • (Recall that a result of the Kinetic Theory of Gases is that the temperature, in degrees Kelvin, is directly proportional to the average kinetic energy of the molecules.)

• Cathode Rays

  • By the time the tube was dark, most of the electrons could travel in straight lines from the cathode to the anode end of the tube without a collision.
  • Through his experiments, Thomson disproved Dalton's atomic theory, because Dalton's atomic theory stated that atoms were the smallest piece of the matter in the universe and they were indivisible.
  • Clearly, the presence of electrons negated these portions of Dalton's atomic theory.
  • Thompson's work disproved John Dalton's theory of the atom.

• Aurora Borealis and the Aurora Australis

  • They are ionized or excited by the collision of solar wind and magnetospheric particles (such as high energy protons and electrons) funneling down and accelerating along the Earth's magnetic field lines.
  • In the vacuum of space, they maintain their energy because the normal method of energy loss, collision, is not possible due to the low particle density.
  • Collisions with other atoms or molecules can absorb the excitation energy and prevent emission.
  • Because the very top of the atmosphere has a higher percentage of oxygen and is sparsely distributed, collisions preventing emission are rare enough to allow oxygen the time needed to emit red light.
  • Collisions become more frequent farther down in the atmosphere, and red emissions do not have time to happen; eventually, even green light emissions are prevented.