Thursday, June 18, 2009

[Chemistry Form 5] Collision Theory

  • The collision theory is based on the kinetic theory, which states that molecules are in constant random motion.

  • In order for a reaction to occur, the reactant molecules must collide in the correct orientation, and with enough energy to form products.

  • Collision between particles that produce a chemical change are called "effective collisions". This is when the reactant molecules collide with enough kinetic energy to break their original bonds and then form new bonds in the product molecules.

  • Effective collision frequency is the number of effective collisions per unit time.

  • The activation energy Ea, is the minimum energy the colliding reactant particles must have before any collision between them can result in a chemical reaction.

The Collision theory, proposed by Max Trautz and William Lewis in 1916 and 1918, qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions.

This theory is based on the idea that reactant particles must collide for a reaction to occur, but only a certain fraction of the total collisions have the energy to connect effectively and cause the reactants to transform into products.

This is because only a portion of the molecules have enough energy and the right orientation (or "angle") at the moment of impact to break any existing bonds and form new ones. The minimal amount of energy needed for this to occur is known as activation energy.

Particles from different elements react with each other by releasing activation energy as they hit each other.

If the elements react with each other, the collision is called successful, but if the concentration of at least one of the elements is too low, there will be fewer particles for the other elements to react with and the reaction will happen much more slowly.

As temperature increases, the average kinetic energy and speed of the molecules increases but this only slightly increases the number of collisions.

The rate of the reaction increases with temperature increase because a higher fraction of the collisions overcome the activation energy.

Collision theory is closely related to chemical kinetics.

Reaction rate tends to increase with concentration -
a phenomenon explained by collision theory

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