Chemical Kinetics (continued)

Collision theory

Atoms of reagent molecules are always in motion, generating many collisions (shocks). Part of these collisions increase the speed of the chemical reaction.

The more shocks with energy and proper geometry, the faster the reaction. There are two types of collisions:

- horizontal - slower collision
- vertical - faster collision, effective collision

See the two collision models for the formation of two HCl molecules:

Horizontal collision

Note that after the first collision only one HCl molecule is formed. The second molecule will form in the second collision.

Vertical collision

Notice that the molecule of H2 approaches the Cl molecule2 very fast. Then they hit each other violently, forming two rapidly moving HCl molecules.

The first collision forms the activated complex (two HCl molecules). This collision happens very fast and therefore faster, more effective. Makes the chemical reaction faster.

The intermediate state of the reaction where the activated complex forms is a transition state where there is a high energy value involved. O activated complex It is the chemical species with the highest energy value in the entire chemical reaction that has a very short life.