1. Reaction Rates

2. What does rate mean?
measure of the speed of any change that occurs within an interval of time
time can range from microseconds (explosions) to centuries (plants to coal)
in chemistry…reaction rate is usually expressed as the amount of the reactant changes per unit time
3 moles/year
5 grams/second

3. Collision Theory
only a small fraction of collisions produce a chemical reation
“effective collisions” have enough kinetic energy and the collide at the correct angle
need enough KE to
assemble new compounds
break the bonds of existing compounds

6. Activation Energy
minimum energy that colliding particles must have in order to react
an activated complex is an unstable compound that forms momentarily at the peak of the “barrier”
typically about seconds
both reactants reform and new products form
also referred to as the transition state

7. Activation Energy

8. Factors Affecting Reaction Rate
The rate of a chemical reaction depends on:
temperature
increasing temp. increases the frequency of collisions AND the KE necessary to overcome the activation energy barrier

9. http://www. absorblearning. com/media/attachment. action
concentration
increasing the number of particles in a given volume increases the rate a which reactions occur

10. particle size surface area affects the reaction rate
smaller particles have a greater ratio of surface area (x2) to volume (x3)
this increases the amount of reactant exposed for reactions
An iron bar is held in a flame and nothing happens. Iron powder is then blown into the flame and ignites

11. presence of a catalyst
a substance that increases the rate of a reaction without being used up during the reaction

12. inibitors interfere with the action of the catalyst