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.

• Glancing Collisions

  • Glancing collision is a collision that takes place under a small angle, with the incident body being nearly parallel to the surface.
  • All collisions conserve momentum.
  • Collision at glancing angle is called "glancing collision".
  • An inelastic collision is sometimes also called a plastic collision.
  • A "perfectly-inelastic" collision (also called a "perfectly-plastic" collision) is a limiting case of inelastic collision in which the two bodies stick together after impact.

• 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.

• Inelastic Collisions in One Dimension

  • Collisions may be classified as either inelastic or elastic collisions based on how energy is conserved in the collision.
  • In an inelastic collision the total kinetic energy after the collision is not equal to the total kinetic energy before the collision.
  • This is in contrast to an elastic collision in which conservation of total kinetic energy applies.
  • While inelastic collisions may not conserve total kinetic energy, they do conserve total momentum.
  • In such a collision, the colliding particles stick together.

• Overview of Temperature and Kinetic Theory

  • The kinetic theory of gases describes a gas as a large number of small particles (atoms and molecules) in constant, random motion.
  • The kinetic theory of gases describes a gas as a large number of small particles (atoms or molecules), all of which are in constant, random motion.
  • Essentially, the theory posits that pressure is due not to static repulsion between molecules (as was Isaac Newton's conjecture) but rather due to collisions between molecules moving at different velocities through Brownian motion.
  • In kinetic theory, the temperature of a classical ideal gas is related to its average kinetic energy per degree of freedom Ek via the equation:
  • (R: ideal gas constant, n: number of moles of gas) from a microscopic theory.

• 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.

• Phase-Space Density

  • If there are no collisions, ${\cal C}=0$, so
  • The collision term $\nabla_{\bf p} \cdot {\bf F} = 0$ must now be expressed in the lab frame of this equation that is no longer manifestly covariant.
  • One could use it as the source for a scalar theory of gravity, but it would violate the equivalence principle.