I suggest you to get thermal data from NIST (http://webbook.nist.gov/cgi/), where you can get single species properties.

A rough estimation can be done using this equation

Energy of Cr+ = I(Cr) is the ionization of Cr (considering gaseous chromium as reference)

Energy of H2 = 0

Energy of CrH +D(CrH)=E(Cr)+E(H) =1/2 D(H2) => E(CrH)=-D(CrH)+1/2 D(H2)

Energy of Cr+ = E(CrH)+I(CrH)

Where E(X), I(X) and D(X) are respectively the energy, dissociation energy and ionization energy of of the X species. This quantities can be find on NIST DB

As a result you

DH(reaction)=-2D(CrH)+1/2 D(H2)+2I(CrH)-2I(Cr)

To be more precise, to this contribution you have to add the internal contribution that depends on the temperature. You can find some internal values on the mist DB too.

Dear Colonna,

Thanks for the help and the indication of the site.

Regards

You are welcome

Gianpiero