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Energy Levels Energy Levels

C7 energy levels

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Page 1: C7 energy levels

Energy LevelsEnergy Levels

Page 2: C7 energy levels

Energy LevelsEnergy Levels

Exothermic reactions

• Energy is given out

• The products have less energy than the reactants

Combustion and neutralisation are exothermic

Page 3: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Exothermic reactions

energy

Page 4: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Exothermic reactions

energy

course of reaction

Page 5: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Exothermic reactions

energy

course of reaction

reactants

Page 6: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Exothermic reactions

energy

course of reaction

reactants

products

Page 7: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Exothermic reactions

energy

course of reaction

reactants

products

energy given out

∆H is negative

Page 8: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

• Energy is taken in

• The products have more energy than the reactants

The energy is taken in from the surroundings

Page 9: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

energy

Page 10: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

energy

course of reaction

Page 11: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

energy

course of reaction

reactants

Page 12: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

energy

course of reaction

reactants

products

Page 13: C7 energy levels

Energy Level DiagramsEnergy Level Diagrams

Endothermic reactions

energy

course of reaction

energy taken in∆H is positivereactants

products

Page 14: C7 energy levels

Summary TableSummary Table

Exothermic reactions

Endothermic reactions

Page 15: C7 energy levels

Summary TableSummary Table

Exothermic reactions

Endothermic reactions

Energy is given out to the surroundings

Energy is taken in from the surroundings

Page 16: C7 energy levels

Summary TableSummary 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

Page 17: C7 energy levels

Summary TableSummary 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

Page 18: C7 energy levels

∆∆HH

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

Page 19: C7 energy levels

Bond energiesBond 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

Page 20: C7 energy levels

Working out ∆HWorking out ∆H

Draw an energy level diagram with all the reactants and products on it

energy

course of reaction

2H2 + O2

2H2O

Page 21: C7 energy levels

Working out ∆HWorking out ∆H

Show all the bonds in the reactants

energy

course of reaction

2H2O

H―HH―H

O=O+

Page 22: C7 energy levels

Working out ∆HWorking out ∆H

Show all the bonds in the products

energy

course of reaction

H―HH―H

O=O+

H HO

H HO

Page 23: C7 energy levels

Working out ∆HWorking out ∆H

Show the bond energies for all the bonds

energy

course of reaction

436436

O=O+

H HO

H HO

Page 24: C7 energy levels

Working out ∆HWorking out ∆H

Show the bond energies for all the bonds

energy

course of reaction

436436

498+

H HO

H HO

Page 25: C7 energy levels

Working out ∆HWorking out ∆H

Show the bond energies for all the bonds

energy

course of reaction

436436

498+

H HO

464 464+

Page 26: C7 energy levels

Working out ∆HWorking out ∆H

Show the bond energies for all the bonds

energy

course of reaction

436436

498+

464 464+

464 464+

Page 27: C7 energy levels

Working out ∆HWorking out ∆H

Add the reactants’ bond energies together

energy

course of reaction

464 464+

464 464+

1370

Page 28: C7 energy levels

Working out ∆HWorking out ∆H

Add the products’ bond energies together

energy

course of reaction

1370

1856

Page 29: C7 energy levels

Working out ∆HWorking out ∆H

∆H = energy in ― energy out

energy

course of reaction

1370

1856

13701856

Page 30: C7 energy levels

Working out ∆HWorking out ∆H

∆H = energy in ― energy out

energy

course of reaction

1370

1856

13701856-486

Page 31: C7 energy levels

Working out ∆HWorking out ∆H

∆H = energy in ― energy out

energy

course of reaction

1370

1856

∆H = -486

Page 32: C7 energy levels

Working out ∆HWorking 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

∆H is energy in – energy out

• Energy goes in to break bonds

• Energy goes out when bonds are made