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Exothermic reaction | Endothermic reaction |
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Heat energy is released into the surroundings | Heat energy is absorbed from the surroundings |
Bond making reactions | Bond breaking reactions |
Surrounding temperature increases | Surrounding temperature decreases |
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Energy level diagrams show the relative energies of the reactant and product.
The energy change of a reaction is represented through the difference in height between the reactant and its product.
Activation energy: the minimum energy required for the reaction to take place
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Endothermic energy level diagram:
Energy is gained by the system; higher activation energy required
Exothermic energy level diagram:
Energy is lost by the system; lower activation energy required
Bond Energy
This is the amount of energy required or released when a bond is formed or broken respectively. The unit measure of this energy is kJ/mol.
Formula for energy change:
%%If overall heat energy value is negative, reaction is exothermic%%
%%If overall heat energy value is positive, reaction is endothermic%%
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%%A good fuel is:%%
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Advantages | Disadvantages |
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Releases a lot of energy | Difficult to transport as it is a gas at room temperature |
Does not produce pollutants | Forms explosive mixture with air when stored under pressure |
Renewable and abundant | Is expensive to produce (requires a lot of energy) |
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%%Fuel Cell%%
Reaction at anode:
2H2 → 4H+ + 4e-
Reaction at cathode:
4H+ + O2 + 4e- → 2H2 O
The flow of the electrons, through the electric circuit, from the cathode to the anode generates a current.
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