I read this problem in a book :

We are given the reaction : H+H ----- H2 + 5ev
where H is the hydrogen atom and H2 is the hydrogen molecule . 5ev of energy is released in the reaction.

However it is not possible to form H2 by simply colliding two H atoms in vaccum. They would simply "bounce off". The author asked us to prove this by using laws of conservetion of momentum and energy.
He asked to show that the initial momentum would have to satisfy an impossible condition in order to release the energy. But i cannot find it.

PLEASE ANSWER!

Question

I read this problem in a book :

We are given the  reaction : H+H -----> H2 + 5ev
where H is the hydrogen atom and H2 is the hydrogen molecule . 5ev of energy is released in the reaction.

However it is not possible to form H2 by simply colliding two H atoms in vaccum. They would simply "bounce off". The author asked us to prove this by using laws of conservetion of momentum and energy.
He asked to show that the initial momentum would have to satisfy an impossible condition in order to release the energy.  But i cannot find it.

PLEASE ANSWER!