Q. Why is there a sudden rise in the graph after a point at minimum energy when the bond formed?

Fig. 4.8 The potential energy curve for the formation of H 2
molecule as a function of internuclear distance of the H atoms.
The minimum in the curve corresponds to the most stable state of
H 2  


Dear student,

This potential energy diagram is one of the most important graph of Chemical Bonding. 
The graph starts from right which assumes that at infinite separation Potential energy is close to zero. As the two atoms approach towards each other, the Potential energy decreases due to attraction( Energy is released on attraction) till the point where it reaches its minimum value and a chemical bond is formed. After this point, if we move the atoms more closely to each other, the repulsion between the two nuclei becomes more dominant than the attraction and the energy increases. At sufficiently close position, due to much high repulsion the energy increases drastically indicating that such an arrangement can only be possible if we somehow supply that much amount of energy. It is not possible spontaneously.

In certain experiments, we require products that are sometimes unstable(having higher energy) to make certain amount of products from that state. 

Hope this helps,


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