Question

Which reaction would occur more readily? Why?

1) Mg + Cl2 --> MgCl2
2) 2Mg + O2 --> MgO

Thanks!

Answer 1

I don't believe there is enough information from what you have posted to determine the rate of either reaction.

At first glance, however, and with what I know, I might think 1 but remember that every piece of Mg ribbon I've seen comes with a thin layer of MgO already deposited. It may have taken weeks to form there If you clean the ribbon and expose a fresh surface of Mg to both O2 and Cl2, THEN 1 probably occurs more easily because the electronegativity of Cl2 is higher than that of O2 AND the activation energy of Mg + O2 is higher than that of Mg + Cl2.