Chemical Kinetics and Equilibrium

1. Chemical Kinetics and Equilibrium Chemistry 2007-2008

2. Chemical Kinetics The study of reaction rates and the factors influencing the rates Reaction rate: The change of concentration of a reactant or product in a unit of time.

3. Collision Theory • Used to explain reaction rates. • Collision theory states that molecules must collide in order to react. • The more collisions there are in a unit of tim, the faster the reaction.

4. Not all collisions will result in a reaction. • Collisions that result in a reaction are said to be “effective”. • For an effective collision: • The molecules must collide with enough energy to react. • The molecules must collide with the proper orientation.

5. The minimum energy required to react is called the activation energy. On a potential energy diagram, this is the difference in energy between the reactants and the high point on the curve.(Ea)

6. 2NOBr  2NO + Br2 Bromine Nitrogen Oxygen NOBr + BrON  NO + BrBr + ON   BrON + NOBR    The molecules will not react because the bromine do not touch each other in this collision to form a new bond.

7. Lab: Measuring Reaction rates: • Informal lab write up: Name Date Partner Title Purpose Data table: Answer questions

8. Factors that affect reaction rates: • Temperature An increase in temperature will cause the reaction rate to increase. This is because: 1. The molecules are moving faster and will collide more frequently. 2. The molecules have more energy when they collide so the collision is more likely to be effective. (or result in a reaction)

9. 2. Concentration An increase in concentration will cause the reaction rate to increase. This is because if there are more molecules then there will be more collisions.

10. 3. Pressure An increase in pressure on a gaseous reaction will cause the rate to increase, This is because it is the collisions of the gas which cause pressure. If pressure increases, then the number of collisions increases. One way to increase pressure is to decrease volume (Boyle’s Law). If the volume is decreased, the molecules will be closer together and there will be more collisions.

11. 4. Surface area If the suface area of a solid is increased ( the solid is ground up.), the reaction rate will increase. This is because more of the solid molecules are available on the suface to react. This results in more collision.

12. 5. Catalyst A catalyst is a substance that speeds up a reaction, but is not used up during the reaction. A catalyst speeds up a reaction by lowering the activation energy. If the activation energy is lowered more collisions will have enough energy to be effective. One way a catalyst can work is by helping to hold the molecules in the correct orientation to react/