1. 5.Energy Change and Chemical Reactions (Con’t)  A kinetic energy distribution curve shows the kinetic energy of collisions in a particular system.  Not all collisions in a system have the same kinetic energy T1T1 EAEA  The temperature of this system is T 1 (average kinetic energy of the system)

2. T1T1 EAEA  Only collisions with KE ≥ E A will be successful.  At a higher temperature (T 2 ) more collisions will have sufficient KE to be successful. T1T1 EAEA T2T2  See page 500 in your textbook.

3. 6.Catalysts  A catalyst speeds up a reaction by decreasing the amount of activation energy required. eg: 2 HI (g) + Energy  H 2(g) + I 2(g) HH EAEA EAEA HH

4. H I H I catalyst  Catalysts increase efficiency of collisions by assisting molecules to collide. eg: H I H I HH II ++  H I H I H I H I H I H I

5.  The only way activation energy can be decreased for any given reaction is by using a catalyst.  Examples: a)Enzymes in living systems Allow reactions to take place at low temperatures (eg: 37  C) b)Many different metal surfaces act as catalysts Palladium and platinum in catalytic converters (they speed up complete combustion of hydrocarbons) Nickel is used to speed up hydrogenation of unsaturated fats (to make them solid)