Question

How can you best describe the transfer of heat that occurs when 1.40 mol of `H_2` reacts?

Answer 1

Well, you can start by specifying with what reagent the dihydrogen reacts.

Explanation:

I think (and I acknowledge I might be wrong) that you refer to a combustion reaction:

`H_2(g) + 1/2O_2(g) rarr H_2O(l)+Delta`

Now I know for a fact that `DeltaH^@""_f(H_2O)=-285*kJ*mol^-1`

And thus if `1.4*mol` `"dihydrogen"` react with `0.7*mol` `"dioxygen"` we get out `1.4*molxx(-285)*kJ*mol^-1~=400*kJ`