Bond Energies and Energy Changes Flashcards

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What is meant by the term bond energy?

Bond energy is the energy needed to break one mole of a type of bond in gas molecules.

What unit is bond energy usually given in?

Bond energy is usually given in kilojoules per mole, written as kJ/mol.

Is breaking chemical bonds an endothermic or exothermic process?

Breaking chemical bonds is endothermic because energy must be taken in.

Is making chemical bonds an endothermic or exothermic process?

Making chemical bonds is exothermic because energy is given out.

In terms of bond energies, why is a reaction exothermic overall?

A reaction is exothermic if the total energy released when new bonds form is greater than the total energy taken in to break bonds.

In terms of bond energies, when is a reaction endothermic overall?

A reaction is endothermic if more energy is taken in to break bonds than is released when new bonds form.

What does the word ‘average’ mean in ‘average bond energy’?

It means the value is an average bond energy for that bond type taken from many different compounds.

What does a larger bond energy value tell you about a bond?

A larger bond energy means the bond is stronger and needs more energy to break.

Why are bond energy values always written as positive numbers?

They are always positive because they show the energy needed to break bonds, not the energy released.

How do you calculate the overall energy change of a reaction using bond energies?

Add up the energies of all bonds broken, add up the energies of all bonds made, then do: energy in (bonds broken) minus energy out (bonds made).