Bond making bond breaking

Energy is needed when bonds are broken. However energy is released when bonds are formed.

Lets take hydrated copper sulfate for example. Its formula is given as CuSO4.6H2O. It shows that for each CuSO4 unit 6 water molecules are bonded via ion-dipole bonding. To drive the water out we supply energy in the form of heat in order to break the bonds ion-dipole bonds.

 

The water molecules bonded to the copper make the crystal appear blue.

 

Once the water is removed the copper sulfate is grey in colour.

When water is added to the crystals, energy is released as ion-dipole bonds form.

Click to see the energy released when water is added to anhydrous copper sulfate.