[Soyeon]

Hi, i have one question from my Hess's law lab report.
△H1: Mg(s)+ 2H+(aq) -> Mg2+ (aq) + H2(g)
△H2: MgO(s) + 2H+(aq) -> Mg2+ (aq) + H2O (l)

I got 2 △H values experimentally. △H is -59.09 kj/mol, -143.45 kj/mol respectively.

But one of my lab question says " find the literature value of △H for the reaction

H2(g) + 1/2O2(g) -> H2O(l)  △H3

Combine three reaction equations and corresponding values for △H
to determine the value for the heat of formation of MgO.

And the equation of △H°f is
Mg(s) + 1/2O2(g)  -> MgO(s)


I have no idea what literature value means and how to calculate △H3
even though I don't have experimental value of that.
Can anyone help me?

[sjb]

The literature value is the commonly accepted value for the reaction or process

If you have this, can you construct a cycle using the principles of Hess' law to get what you want?

[Borek]

I have no idea what literature value means

One cited in literature - in other words, you are expected to find a book where ΔH values are listed and find the value for your reaction.

[Enthalpy]

The sought reaction forms H₂O from its elements, so the heat (or enthalpy) of reaction is also the heat of formation of H₂O.

Tables in books (=literature values) use to give heats of formations for varied compounds from their elements in the standard state, because you can deduce (many more) heats of reaction from (fewer) heats of formation.

For instance the "CRC Handbook of Chemistry and Physics" contains such a table.

Pay attention to the state of the compounds: is it liquid or gaseous water?