Question

help please. let me attach the question!

Answer 1

Farmiliar with Hess's law?

Answer 2

no lol.

Answer 3

can you tell me how?

Answer 4

I sure can. Hess's law states:
"The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divided."
plus you should know the relation: for a reaction A -> B it follow that:
\[\Delta H(A \rightarrow B)=- \Delta H(B \rightarrow A)\]
So we set up an expression for the wanted equation using part processes:
\[H _{2}O(s) ~ + ~ H _{2}O(l) \rightarrow H _{2}(g) ~ + ~ \frac{ 1 }{ 2 } O _{2}(g) ~ + ~ H _{2}O(l)\]
We notice that the H2O(l) cancels on both sides and we get the wanted reaction. Hess law then tell us:
\[\Delta H _{r} = \Delta H(H _{2}O(l) \rightarrow H _{2}O(s))+\Delta H(H _{2}O(l) \rightarrow \frac{ 1 }{ 2 } O _{2}(g))\]
We now talk about the 1. reaction as A and the other as B, but using the relation I wrote we then get:
\[\Delta H _{r}=- \Delta H(A)+(-\Delta H(B))\]