Question

Calculate the enthalpy change, ∆H in kJ, for the reaction H2O(s) → H2(g) + 1/2O2(g)



Answer 1



Answer 2

you have to combine the equations in such a way that you're only left with what they asked.

by inverting the 1st equation you get \(H_2O_{(l)}\rightarrow 1/2O_{2\;(g)}+H_{2\;(g)}\)

when you add the 1st and the 2nd (and cancel out repeating species), you're left with the equation you need.

In terms of enthalpy, this translates into multiplying the 1st equation by -1, then adding up both of the values.