.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/thermo/thermochemistry/plot_01_hess_law.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_thermo_thermochemistry_plot_01_hess_law.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_thermo_thermochemistry_plot_01_hess_law.py:


Hess's law: reaction enthalpy does not depend on the path
=========================================================

Burning graphite straight to :math:`CO_2` releases the same heat as
burning it first to :math:`CO` and then burning the :math:`CO`. The
enthalpy-level diagram below shows both routes, summed with
:func:`~chemistrykit.thermo.systems.thermochemistry.hess_law_enthalpy`.
The same principle lets
:func:`~chemistrykit.thermo.systems.thermochemistry.reaction_enthalpy_from_formation`
compute any reaction enthalpy from tabulated enthalpies of formation,
shown here for the combustion of methane.

.. GENERATED FROM PYTHON SOURCE LINES 16-41

.. code-block:: Python

    import matplotlib.pyplot as plt

    from chemistrykit.thermo.systems.thermochemistry import hess_law_enthalpy, reaction_enthalpy_from_formation

    dH_C_to_CO = -110.5  # C(graphite) + 1/2 O2 -> CO, kJ/mol
    dH_CO_to_CO2 = -283.0  # CO + 1/2 O2 -> CO2
    dH_direct = hess_law_enthalpy([1.0, 1.0], [dH_C_to_CO, dH_CO_to_CO2])

    levels = {"C + O2": 0.0, "CO + 1/2 O2": dH_C_to_CO, "CO2": dH_direct}
    fig, ax = plt.subplots(figsize=(7, 5))
    for x, (label, H) in zip([0.0, 1.0, 2.0], levels.items()):
        ax.hlines(H, x - 0.3, x + 0.3, color="black", linewidth=2)
        ax.text(x, H + 10, label, ha="center")
    ax.annotate("", xy=(1.0, dH_C_to_CO), xytext=(0.0, 0.0), arrowprops=dict(arrowstyle="->", color="steelblue"))
    ax.annotate("", xy=(2.0, dH_direct), xytext=(1.0, dH_C_to_CO), arrowprops=dict(arrowstyle="->", color="steelblue"))
    ax.annotate("", xy=(2.0, dH_direct), xytext=(0.0, 0.0), arrowprops=dict(arrowstyle="->", color="crimson"))
    ax.text(0.35, -70, f"{dH_C_to_CO} kJ/mol", color="steelblue")
    ax.text(1.55, -230, f"{dH_CO_to_CO2} kJ/mol", color="steelblue")
    ax.text(0.7, -300, f"direct: {dH_direct} kJ/mol", color="crimson")
    ax.set_xlim(-0.6, 2.6)
    ax.set_xticks([])
    ax.set_ylabel("enthalpy (kJ/mol)")
    ax.set_title("Two routes from graphite to CO2, one enthalpy change")
    fig.tight_layout()




.. image-sg:: /api/gallery/thermo/thermochemistry/images/sphx_glr_plot_01_hess_law_001.png
   :alt: Two routes from graphite to CO2, one enthalpy change
   :srcset: /api/gallery/thermo/thermochemistry/images/sphx_glr_plot_01_hess_law_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 42-44

Methane combustion, :math:`CH_4 + 2O_2 \to CO_2 + 2H_2O(l)`, from
standard enthalpies of formation (kJ/mol):

.. GENERATED FROM PYTHON SOURCE LINES 44-51

.. code-block:: Python


    dHf = {"CH4": -74.8, "O2": 0.0, "CO2": -393.5, "H2O(l)": -285.8}
    dH_comb = reaction_enthalpy_from_formation([-1, -2, 1, 2], list(dHf.values()))
    print(f"Two-step graphite combustion: {dH_direct:.1f} kJ/mol")
    print(f"Methane combustion from formation enthalpies: {dH_comb:.1f} kJ/mol")

    plt.show()




.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    Two-step graphite combustion: -393.5 kJ/mol
    Methane combustion from formation enthalpies: -890.3 kJ/mol





.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.038 seconds)


.. _sphx_glr_download_api_gallery_thermo_thermochemistry_plot_01_hess_law.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_01_hess_law.ipynb <plot_01_hess_law.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_01_hess_law.py <plot_01_hess_law.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_01_hess_law.zip <plot_01_hess_law.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

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