Energy Levels
A
Creative Chemistry
PowerPoint Presentation
By Nigel Saunders
Copyright © 2003 Nigel Saunders, all rights reserved
Permission is granted for personal and educational use only.
Commercial copying, hiring, lending is prohibited.
Energy Levels
Exothermic reactions
• Energy is given out
• The products have
less energy than the
reactants
Combustion and neutralisation are exothermic
Energy Level Diagrams
Exothermic reactions
energy
Energy Level Diagrams
Exothermic reactions
energy
course of reaction
Energy Level Diagrams
Exothermic reactions
energy
reactants
course of reaction
Energy Level Diagrams
Exothermic reactions
energy
reactants
products
course of reaction
Energy Level Diagrams
Exothermic reactions
energy
reactants
energy given out
∆H is negative
products
course of reaction
Energy Level Diagrams
Endothermic reactions
• Energy is taken in
• The products have
more energy than
the reactants
The energy is taken in from the surroundings
Energy Level Diagrams
Endothermic reactions
energy
Energy Level Diagrams
Endothermic reactions
energy
course of reaction
Energy Level Diagrams
Endothermic reactions
energy
reactants
course of reaction
Energy Level Diagrams
Endothermic reactions
energy
products
reactants
course of reaction
Energy Level Diagrams
Endothermic reactions
energy
products
reactants
energy taken in
∆H is positive
course of reaction
Summary Table
Exothermic
reactions
Endothermic
reactions
Summary Table
Exothermic
reactions
Energy is given out to
the surroundings
Endothermic
reactions
Energy is taken in from
the surroundings
Summary Table
Exothermic
reactions
Endothermic
reactions
Energy is given out to
the surroundings
Energy is taken in from
the surroundings
∆H is negative
∆H is positive
Summary Table
Exothermic
reactions
Endothermic
reactions
Energy is given out to
the surroundings
Energy is taken in from
the surroundings
∆H is negative
∆H is positive
Products have less
energy than reactants
Products have more
energy than reactants
∆H
How much energy is given out or taken in?
• Energy is needed to break chemical bonds
• Energy is given out when bonds are made
∆H is the difference between the energy
needed to break the bonds in the reactants,
and the energy given out when new bonds are
made in the products
Bond energies
The energy needed to break a chemical bond
• Different chemical bonds have different
bond energies
Chemical bond
Bond energy, kJ/mole
H―H
436
O=O
498
O―H
464
Working out ∆H
Draw an energy level diagram with all the
reactants and products on it
energy
2H2 + O2
2H2O
course of reaction
Working out ∆H
Show all the bonds in the reactants
energy
H―H
H―H
+ O=O
2H2O
course of reaction
Working out ∆H
Show all the bonds in the products
energy
H―H
H―H
+ O=O
H
H
O
O
course of reaction
H
H
Working out ∆H
Show the bond energies for all the bonds
energy
436
436
+ O=O
H
H
O
O
course of reaction
H
H
Working out ∆H
Show the bond energies for all the bonds
energy
436
436
+ 498
H
H
O
O
course of reaction
H
H
Working out ∆H
Show the bond energies for all the bonds
energy
436
436
+ 498
464 + 464
H
O
course of reaction
H
Working out ∆H
Show the bond energies for all the bonds
energy
436
436
+ 498
464 + 464
464 + 464
course of reaction
Working out ∆H
Add the reactants’ bond energies together
energy
1370
464 + 464
464 + 464
course of reaction
Working out ∆H
Add the products’ bond energies together
energy
1370
1856
course of reaction
Working out ∆H
∆H = energy in ― energy out
energy
1370
―
1856
1370
1856
course of reaction
Working out ∆H
∆H = energy in ― energy out
energy
1370
―
1856
-486
1370
1856
course of reaction
Working out ∆H
∆H = energy in ― energy out
energy
1370
∆H = -486
1856
course of reaction
Working out ∆H
Summary
• The energy values have units of kJ/mole
• In the exam, you will be given the energy
values and all the bonds to make or break
• Energy goes in to break bonds
• Energy goes out when bonds are made
∆H is energy in – energy out