2.  When molecules or other particles of substances collide, they may react. The speed, or rate, of a given reaction depends upon several things

3.  People attempt to change the speed at which reactions take place in many situations ◦ Spoiling of food and rusting of cars involve reactions that people try to slow down.

4.  Area of chemistry dealing with the speed at which reactions take place.  The speed of a reaction depends upon two or more molecules colliding in such a way that old bonds break and new bonds form

5.  The materials used in a chemical reaction often determine its rate.  Example Hydrogen and oxygen combine quickly and explosively to form water. However oxygen reacts slowly with iron to form rust.

6.  As temperature increases, the average kinetic energy or speed, of reacting particles increases.  This results in more collisions between particles

7.  Reactions take place when surfaces are in contact.  Crushing a solid reactant into small pieces is a way to increase its surface area  More surface area allows more contact between the reactants, and a faster reaction takes place.

8.  Increasing the concentration of one or more reactants increases the number of possible collisions between the reacting particles.  Thus greater concentration of reactants, the greater the reaction rate.

9.  Something that speeds a chemical reaction without itself being permanently changed  It is a substance that increases the rate of reaction without being consumed in the reaction.  It provides an easier way for the chemical reaction to occur. It does this by decreasing the energy needed to break bonds and form new ones.