Energy Level Diagrams'

1
Energy Level Diagrams.
1. Exothermic reactions.
2
Energy is put in to break the bonds holding the
atoms together.
Energy (kJ)
Reactants

• The reactants are bonded together

• Energy is stored in these bonds.

3
To break the H-H bond you need 436 kJ mol-1.
This is called the Activation Energy.
Energy (kJ)
To break the Cl-Cl bond you need 243 kJ mol-1.
Reactants
4
Molecules become Atomised
H
Cl
Cl
H
Energy (kJ)
Reactants
5
Molecules become Atomised
H
Cl
Cl
H
Energy (kJ)
Reactants
6
Molecules become Atomised
H
Cl
Cl
H
Energy (kJ)
Reactants
7
Molecules become Atomised
H
Cl
Cl
H
Energy (kJ)
Reactants
8
Molecules become Atomised
The newly formed bonds have less energy
Energy (kJ)
Reactants
Products
9
Energy (kJ)
-432 kJ mol-1each
Reactants
Products
10
Summary
Molecules become Atomised
Energy in 678 kJ
Energy released -862 kJ
DH -184 kJ
Products
11
Energy (kJ)
Reactants
Energy difference DH -184 kJ
Products
12
Energy Level Diagrams.
2. Endothermic reactions.
13
Energy is put in to break the bonds holding the
atoms together.
Energy (kJ)
Reactants

• The reactants are bonded together

• Energy is stored in these bonds.

14
To break the O-H bond you need 464 kJ mol-1 each.
This is called the Activation Energy.
Energy (kJ)
To break the O-H bond you need 464 kJ mol-1 each.
Reactants
15
Molecules become Atomised
O
O
H
H
H
H
Energy (kJ)
Reactants
16
Molecules become Atomised
O
O
H
H
H
H
Energy (kJ)
Reactants
17
Molecules become Atomised
O
O
H
H
H
H
Energy (kJ)
Reactants
18
Molecules become Atomised
O
O
H
H
H
H
Energy (kJ)
Reactants
19
Molecules become Atomised
O
O
H
H
H
H
Energy (kJ)
Reactants
20
Molecules become Atomised
O
H
O
H
H
H
Energy (kJ)
Reactants
21
Molecules become Atomised
H
O
H
O
H
H
Energy (kJ)
Reactants
22
Molecules become Atomised
Energy (kJ)
The new bonds have more energy stored in them
than before.
Reactants
23
Energy released when OO bonds are formed is 498
kJ mol-1 each.
Energy (kJ)
Reactants
Energy released when H-H bonds are formed is 436
kJ mol-1 each.
24
Summary
Molecules become Atomised
Energy released 1368 kJ
Energy in 1852 kJ
Energy (kJ)
Reactants
25
Energy (kJ)
Products
Reactants
Energy Difference DH 84kJ