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CHEMISTRY UNIT 8 - ENERGY CHANGES (Exothermic ex (Change in energy shown…
CHEMISTRY UNIT 8 - ENERGY CHANGES 
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Exothermic
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Endothermic
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Eg. Thermal decomposition - heating calcium carbonate causes it to decompose into Calcium Oxide & CO2
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ΔH is greater than zero because the energy of the reactants is less than the energy of the products. Energy is absorbed in the reaction.
Activation energy
Activation energy is the minimum energy required to start a chemical reaction or ignite a combustible vapor, gas or dust cloud.
Represented on an energy level diagram as the difference between the reactants’ energy level and the top of the curve.
For example, burning methane in a Bunsen burner:
methane + oxygen → carbon dioxide + water
The activation energy must be supplied in the form of a flame or a spark to get the methane to ignite.
Bond Making
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Bond Breaking
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Reaction Profiles
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Diagrams that show the relative energies of the reactants, products in a reaction & how energy changes over the course of the reaction