I do not understand why the two volumes are added instead of subtraction .The picture is attached herewith.(Refer to the place where H=U+PV and delta V is sum of all components).That is the place I am stuck up with.
It should indeed be VMO - (1/2)VO2-VM
Whoever added the three volumes made an error. Differences are always (sum of product values) -( sum of reactant values).
Looks like an isothermal process: Ti = Tf, and therefore delta-H = 0, and q = -w.
Aside from this, your P x delta-V term will depend upon the delta-n moles of gas in going from reactants to products. Careful with the sign conventions. Delta-n = -2!
PS. The volume changes for condensed phases (solids and liquids) are minuscule compared to volume changes associated with the formation or consumption of gas phase components in a given reaction.
Antoni Peters why would ΔH be zero for an isothermal process? We are talking about standard enthalpies of reaction here. For the reaction Pb + (1/2)O2 -> PbO for instance this is equal to ΔfHo = -218 kJ at 300K. A lot of heat is generated.
Even if it were 0, it is not H = q+w, but ΔU.
Also the metal is not specified, and the temperature is 1000K, some metals have a decent vapor pressure at that temperature.
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