Standard Reaction Enthalpy

[amreen_sandhu1k]

In lecture, we discussed that the standard enthalpy of formation of an element in its most stable form is zero. Would that mean that the standard enthalpy of formation for C(gr) + O2(g) --> CO2(g) would be zero?

[905783577]

No, because CO2 is a compound, not an element.

[Reece Fong 2k]

No. That applies to atoms like diatomic gasses that occur naturally at O2, N2, etc.

[Alison King 3L]

Since CO2 is not an element, it would have a nonzero standard enthalpy of formation

[Vivek Chotai 2C]

you are almost correct since the standard enthalpy of C (graphite) and O2 (g) is 0. But remember the standard enthalpy of formation = (sum of standard enthalpies of formation of products) - (sum of standard enthalpy of formations of reactant). So even though your sum of standard enthalpy formations for reactants is 0, you would still need the standard formation enthalpy of CO2, the products. Let's say that value is X, then the standard enthalpy of formation for CO2 would be X - 0, or X.