Question

Where is potential energy seen in chemistry?

Answer 1

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"`

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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.