Rate of Reaction

Rates of chemical reactions Reaction rate - how quickly reactants turn into products

Collision Theory - theory that reacting molecules must collide with sufficient energy and orientation if they are to form products

Collision theory explains why the rate of reaction is affected by four factors concentration surface area temperature and catalysts.

Concentration - the amount of a substance in a given unit of volume The higher the concentration, the more (higher frequency) collisions will take place and the reaction rate will increase.

Concentration and particle collisions

Surface Area - the amount of surface of a solid that is exposed. Breaking a solid into smaller pieces exposes more surface area. This increases the number (frequency) of collisions between reacting molecules.

Surface area and particle collisions

Example: Sawdust burns faster than Logs Example: Fine crystals of salt dissolve more quickly than large crystals of rock salt.

Temperature - an increase in temperature usually increases reaction rate. Molecules at high temperature move about faster (have higher kinetic energy) and therefore have more (higher frequency) successful collisions.

Temperature and particle collisions

Catalyst- A catalyst is a compound that increases the chances of a successful collision A catalyst does not take part in the reaction other than to increase the rate of reaction

The “other” one - Pressure If the products and reactants are gasses, then pressure will affect reaction rate. The higher the pressure, the more collisions, and the faster the rate

Particles will have a higher frequency of collisions with more energy. Section Review What is reaction rate? How is reaction rate related to collision theory? Name four factors that affect reaction rate.