How do you find the standard enthalpy change?

Question

How do you determine the standard enthalpy change of the reactions when you are given the following equations?

For example,

Ba(s) + O2 (g) + H2(g) -->Ba(OH)2 (s),
and enthalpy change (delta H) = -946kJ

Answer 1

use this equation

ΔHreaction = ΣΔHf (Products) - ΣΔHf (Reactants)

Σ = Sum of

If you have the (delta H) of the different Chemicals then plug them into the equation.

Answer 2

I think that you mean that the heat of formation of an element in its standard state (metal; or gas at STP) is zero.