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Science C5 - Coggle Diagram
Science C5
Bond Enthalpies
During a chemical reaction, energy must be supplied to break bonds in the reactants and energy is released to form bonds in the products
The energy needed to break bonds and the energy released when bonds are formed can be calculated from bond energies
This image shows that 411kj/mol of energy needs to be put in to break the carbon-hydrogen bond. It also means that 459kj/mol is given out when the oxygen hydrogen bond is made in water.
The difference between the sum of energy needed to break bonds in the reactants and the sum of energy released when bonds in the products are formed is the overall energy change of the reaction
This means that overall energy change = energy needed to break bonds - energy released as bonds are made
In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break bonds
In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds
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Energy Profile Diagrams
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Reaction Energy Profile
This reaction is endothermic because energy is being released. Therefore, the CH,4 and 2O,2, the reactants, must have more energy than the products, CO,2 and 2H,2,O
We can show this information by making something called a reaction profile. On this we need to include the formulae or names of the products and reactants, we also need to show the relative energies of the reactants and products.
This reaction profile will look like this:
You need to add even more information than this onto the profile by adding the activation energy. This is shown by a curved line rising above the reactants energy:
Now you can see the overall change in energy within the reaction: