-All chemical reactions involves △Energy
Some release energy. exothermic
Some absorb energy. endothermic
Molecules are held together by chemical bonds.
-Add energy to break bonds
-Give off energy to join together
Takes MORE enerygy to break down than it gives off to form bonds→Endothermic
Takes LESS energy to break down than it gives off to form bonds→ Exothermic
Enthalpy, H, heat contained in the system.
Energy Diagrams
-Chart the potential energy of the chemicals as they change from reactants to products
-Reactants start with a certain amount of energym energy is added to start the reactions and then energy is released as the reaction proceeds.
-The relative amounts of energy determine: Endothermic & Exothermic.
Energy of reactants: total E of all reactants in the reaction
Energy of products: total E of all products in the reaction
Energy of activated complex: potentioal E of the "transition state" between reactants & products
Activation Energy: The E must be added to get the reaction to progress.
△H: the change in potential energy during the reaction.
△H= E of reactants - E of products
Potential Energy Diagram
E of reactants ＜ E of products E of reactants ＞E of products
△H is positive. △H is negative.
Endothermic reaction Exothermic reaction.
The Energy absorption or release can be placed directly in the equation.
Eg. CH4+2O2→CO2+2H2O+812KJ
Higher E Lower E
Exothermic reactions have the E term on the RIGHT side(RHS) -△H
Endothermic reactions have the E term on the Left side (LHS) +△H
Eg.
E of Reactants= 150 KJ
E of Products= 100KJ
E of Activated complex= 300 KJ
△H=? Ea=?
△H= E products- E reactants
= 100KJ - 150KJ= -50KJ ( exothermic)
Ea= E activated complex - E reactants
= 300KJ - 150KJ= 150KJ
Eg.
E of Reactants （E）=200 KJ
△H（F） =100 KJ ( Endothermic)
Ea(B) =300 KJ
E of activated complex (C) =? E of Product (G)=?
E of activated complex= Ea+ E of reactants= 200KJ+300KJ=500KJ
E of product= E of activated complex- E of reactants= 500 KJ- 200KJ= 300KJ
