.. _sphx_glr_api_gallery_thermo_thermochemistry:

Thermochemistry
---------------

Hess's law of constant heat summation and Nernst's heat theorem: reaction
enthalpies built from steps or formation enthalpies, and the behavior of
reaction entropies and free energies as the temperature approaches
absolute zero.


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  <div id='sg-tag-list' class='sphx-glr-tag-list'></div>


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    <div class="sphx-glr-thumbnails">

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    <div class="sphx-glr-thumbcontainer" tooltip="Burning graphite straight to CO_2 releases the same heat as burning it first to CO and then burning the CO. The enthalpy-level diagram below shows both routes, summed with hess_law_enthalpy. The same principle lets reaction_enthalpy_from_formation compute any reaction enthalpy from tabulated enthalpies of formation, shown here for the combustion of methane.">

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  .. image:: /api/gallery/thermo/thermochemistry/images/thumb/sphx_glr_plot_01_hess_law_thumb.png
    :alt:

  :doc:`/api/gallery/thermo/thermochemistry/plot_01_hess_law`

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      <div class="sphx-glr-thumbnail-title">Hess's law: reaction enthalpy does not depend on the path</div>
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    <div class="sphx-glr-thumbcontainer" tooltip="For a reaction between perfect crystals, Nernst found that \Delta G and \Delta H approach each other with zero slope as T \to 0, so \Delta S = -\partial\Delta G/\partial T \to 0. With Debye T^3 heat capacities, \Delta C_p = \alpha T^3, the curves are \Delta H = \Delta H_0 + \alpha T^4/4, \Delta S = \alpha T^3/3, and \Delta G = \Delta H_0 - \alpha T^4/12. Planck&#x27;s stronger form, S \to 0 for every perfect crystal, gives absolute entropies from calorimetry, S(T) = \int_0^T C_p/T&#x27;\,dT&#x27;. Those absolute entropies underlie the standard Gibbs energies of formation that gibbs_energy_of_mixture takes as input.">

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  .. image:: /api/gallery/thermo/thermochemistry/images/thumb/sphx_glr_plot_02_nernst_heat_theorem_thumb.png
    :alt:

  :doc:`/api/gallery/thermo/thermochemistry/plot_02_nernst_heat_theorem`

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      <div class="sphx-glr-thumbnail-title">Nernst's heat theorem: reaction entropy vanishes at absolute zero</div>
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    </div>


.. toctree::
   :hidden:

   /api/gallery/thermo/thermochemistry/plot_01_hess_law
   /api/gallery/thermo/thermochemistry/plot_02_nernst_heat_theorem