Energy Diagrams (1)
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![Page 1: Energy Diagrams (1)](https://reader036.fdocuments.in/reader036/viewer/2022062421/55cf914c550346f57b8c5430/html5/thumbnails/1.jpg)
ENTHALPY
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OBJECTIVES Exothermic changes cause heat to be
released to the surroundings
Endothermic changes cause absorption of heat from the surroundings.
A potential energy diagram can be used to show the energy pathway for a reaction.
The enthalpy change is the energy difference between products and reactants.
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Enthalpy DiagramsEnthalpy DiagramsExothermic reactions
energy
course of reaction
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Energy Level DiagramsEnergy Level DiagramsExothermic reactions
energy
course of reaction
reactants
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Energy Level DiagramsEnergy Level DiagramsExothermic reactions
energy
course of reaction
reactants
products
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Energy Level DiagramsEnergy Level DiagramsExothermic reactions
energy
course of reaction
reactants
products
energy given out
∆H is negative
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Energy Level DiagramsEnergy Level DiagramsEndothermic reactions
energy
course of reaction
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Energy Level DiagramsEnergy Level DiagramsEndothermic reactions
energy
course of reaction
reactants
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Energy Level DiagramsEnergy Level DiagramsEndothermic reactions
energy
course of reaction
reactants
products
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Energy Level DiagramsEnergy Level DiagramsEndothermic reactions
energy
course of reaction
energy taken in∆H is positivereactants
products
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Summary TableSummary Table
Exothermic reactions
Endothermic reactions
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Summary TableSummary Table
Exothermic reactions
Endothermic reactions
Energy is given out to the surroundings
Energy is taken in from the surroundings
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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
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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
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∆∆HHHow 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
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C
H
H
H H
O O
O O
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C
H
H
H H
O O
O O
Energy absorbed to break bondsEnergy absorbed to break bonds
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C
H
H
H H
O O
O O
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C H
H
H
H O
O
O
O
Energy released when new bonds are madeEnergy released when new bonds are made
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Overall energy changeOverall energy change
==
Energy released on making new bondsEnergy released on making new bonds
--
Energy taken in to break old bondsEnergy taken in to break old bonds
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Energy Level DiagramsEnergy Level DiagramsExothermic reactions
energy
course of reaction
methane + oxygen
carbon dioxide + water
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Reaction mixtureReaction mixture
Test tubeTest tube
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Heat given out to Heat given out to surroundingssurroundings
EXOTHERMICEXOTHERMIC
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Heat taken in from Heat taken in from surroundingssurroundings
ENDOTHERMICENDOTHERMIC
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TASK Draw energy level diagrams for the
following reactions:1. Photosynthesis
2. Calcium with sulphuric acid
3. Dissolving ammonium nitrate