ORGANIC CHEMISTRY 3540

EQUILIBRIA

ENERGY

RATES

INTERMEDIATES

TRANSITION STATES

REACTION COORDINATE DIAGRAMS

EQUILIBRIA, ENERGY, RATES

A + B --> C + D

--RATE IS A FUNCTION OF THE RATE CONSTANT AND CONCENTRATION OF A AND B.

BUT.... C + D --> A + B

--RATE IS A FUNCTION OF THE RATE CONSTANT AND CONCENTRATION OF C AND D.

EVENTUALLY ARRIVE AT A STATE OF EQUILIBRIUM

DESCRIBE WITH THE EQUILIBRIUM CONSTANT

ENTHALPY IS GENERALLY THE LARGER TERM AND MOST IMPORTANT (BUT NOT AT HIGH TEMPERATURES!)

NOTE: FREE ENERGY CHANGES AND EQUILIBRIUM CONSTANTS ONLY TELL US THE POSITION OF EQUILIBRIUM!

THEY DO NOT TELL US HOW FAST EQUILIBRIUM IS ACHIEVED!

CAN GRAPHICALLY SHOW ENERGY CHANGE WITH A REACTION COORDINATE DIAGRAM.

REACTION COORDINATE DIAGRAM FOR CHLORINATION OF METHANE.

TRANSITION STATES

IS THE COMBUSTION OF GASOLINE EXOTHERMIC?

WHY DOESN'T THE GASOLINE IN THE TANK BURN?

IS THE COMBUSTION OF A MATCH EXOTHERMIC?

IS THE REACTION OF SODIUM AND CHLORINE EXOTHERMIC? REACTION MOVIE

NEED TO PROVIDE SOME ENERGY TO START REACTION. CALL THIS ENERGY, THE ACTIVATION ENERGY.

THE LARGER THE ACTIVATION ENERGY, THE SLOWER THE REACTION.

THE ACTIVATION ENERGY ENABLES THE REACTANTS TO REACH SOME STATE AT WHICH THE REACTANTS CAN EASILY GO TO PRODUCTS.

CALL THIS STATE THE TRANSITION STATE.

CAN ALSO GRAPHICALLY SHOW THESE ENERGY CHANGES WITH A REACTION COORDINATE DIAGRAM.

THERE MUST BE AN IDEAL ROUTE FROM REACTANT TO TRANSITION STATE TO PRODUCT.

THAT ENERGY CURVE BECOMES A CRITICAL PART OF THE REACTION COORDINATE DIAGRAM.

CAN HAVE A VARIETY OF REACTIONS WHICH ARE ENDOTHERMIC OR EXOTHERMIC AND FAST OR SLOW.

INTERMEDIATES

SOME REACTIONS ARE MULTISTEPPED.

BUT ..... EACH STEP HAS:

---ITS OWN TRANSITION STATE

---ITS OWN ACTIVATION ENERGY

---ITS OWN FREE ENERGY CHANGE

EASILY SHOWN WITH A REACTION COORDINATE DIAGRAM.

DETERMINE OVERALL ENERGIES.

--answer.