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24.12: The Gibbs Free Energy Change for Forming HI(g) from H₂(g) and I₂(g)

  • Page ID
    152810
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    The standard Gibbs free energies of formation\({}^{1}\) for \(HI\left(g\right)\) and \(I_2\left(g\right)\) are \(1.7\ \mathrm{kJ}\ {\mathrm{mol}}^{-1}\) and \(19.3\ \mathrm{kJ}\ {\mathrm{mol}}^{-1}\), respectively. Calculation of the Gibbs free energy of this reaction from thermochemical data gives \({\Delta }_rG^o\left(298.15\ \mathrm{K}\right)=-15.9\ \mathrm{kJ}\). The difference between this value and the value calculated above is \(0.3\ \mathrm{kJ}\). The magnitude of this difference is consistent with the number of significant figures given for the tabulated thermochemical data. However, some error results because we have used the simplest possible quantum mechanical models for rotational and vibrational motions. The accuracy of the statistical–mechanical calculation can be increased by using models in which the vibrational oscillator does not follow Hooke’s law exactly and in which the rotating molecule is not strictly rigid.


    This page titled 24.12: The Gibbs Free Energy Change for Forming HI(g) from H₂(g) and I₂(g) is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Paul Ellgen via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.