Where is potential energy seen in chemistry?

1 Answer
Jun 1, 2016

The potential energy of a chemical bond is where one might see potential energy.


On the #y# axis, we have the potential energy in #"kJ/mol"#, and on the #x# axis, we have the distance #r# between the left atom (#"H"#) and the right atom (#"H"#)'s nuclei.

  • As the two hydrogen atoms move closer together, the attraction between hydrogen A's valence electron and hydrogen B's proton increases. Same with hydrogen A's proton and hydrogen A's valence electron.

  • An energy of attraction is conventionally negative, so we move downwards on the potential energy curve.

If we move leftwards past the #"74 pm"# mark on the graph:

  • When the two hydrogen atoms are too close, each proton in each nucleus repels the other. This is a nuclear repulsion energy.

  • This energy of repulsion is conventionally positive, so we move upwards on the potential energy curve.

A molecule wants to be as stable as possible; if it is unstable, it breaks apart.

So, the molecule prefers to be at the #"74 pm"# mark, which balances the repulsive and attractive energies, giving us the potential energy of the #"H"-"H"# single bond once the bond forms:

#-"436 kJ/mol"#

This potential energy is the energy leftover, stored in the bond, after making the #"H"-"H"# bond and releasing excess energy.

If the bond breaks, the potential energy is absorbed back into the atoms as kinetic energy as the atoms move far apart.