Chemistry C3 3.4 Calculations using bond energies.

What happens in an exothermic reaction?

The energy released when new bonds are formed is greater than the energy absorbed when bonds are broken.

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What happens in an endothermic reaction?

The energy released when new bonds are formed is less than the energy absorbed when bonds are broken.

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How can the overall energy change is a chemical reaction be calculated?

Using bond energies.

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Why is energy needed for a chemical reaction to take place?

To break the bonds in the reactants.

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What happens to energy when new bonds are formed in products?

It is released.

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What does the difference in the energy changes when bonds are broken and formed in a chemical reaction determine?

Whether the overall reaction is exothermic or endothermic.

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What is bond energy?

The energy needed to break the bond between two atoms is called the bond energy for that bond.

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How are bond energies measured?

In kJ/mol.

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How can bond energies be used to calculate the overall energy change for a reaction?

An equal amount of energy is released when the bond forms between two atoms.

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The balanced equation for the reaction is needed to calculate the energy change for a reaction, therefore what should be calculated?

The total amount of energy needed to break all of the bonds in the reactants, the total amount of energy released in making all of the bonds in the products and the difference between the two totals.

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NEED TO LOOK UP AND PRACTICE ENERGY BOND CALCULATIONS

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Chemistry C3 3.4 Calculations using bond energies.

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