.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/electrochem/standard_potentials/plot_02_stockholm_sign_convention.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_electrochem_standard_potentials_plot_02_stockholm_sign_convention.py>`
        to download the full example code.

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

.. _sphx_glr_api_gallery_electrochem_standard_potentials_plot_02_stockholm_sign_convention.py:


The 1953 Stockholm convention: electrode potentials are reduction potentials
==============================================================================

Before IUPAC's 1953 Stockholm meeting, one tradition tabulated
*oxidation* potentials and another *reduction* potentials, so the same
couple appeared with opposite signs in different books. This example
shows both conventions for the table in
:data:`~chemistrykit.electrochem.systems.standard_potentials.STANDARD_REDUCTION_POTENTIALS`
(which follows Stockholm), and shows that the cathode-minus-anode rule of
:func:`~chemistrykit.electrochem.systems.standard_potentials.cell_potential`
only gives the right cell voltage and spontaneity when both half-reactions
use the agreed reduction convention.

.. GENERATED FROM PYTHON SOURCE LINES 17-23

.. code-block:: Python

    import matplotlib.pyplot as plt
    import numpy as np

    from chemistrykit.electrochem.systems.standard_potentials import STANDARD_REDUCTION_POTENTIALS as T
    from chemistrykit.electrochem.systems.standard_potentials import cell_potential, is_spontaneous








.. GENERATED FROM PYTHON SOURCE LINES 24-25

Correct usage: both values are Stockholm reduction potentials.

.. GENERATED FROM PYTHON SOURCE LINES 25-28

.. code-block:: Python

    E_ok = cell_potential(T["Ag+/Ag"], T["Cu2+/Cu"])
    print(f"Ag+/Ag cathode, Cu anode (both reduction potentials): E = {E_ok:+.2f} V, spontaneous = {is_spontaneous(E_ok)}")





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

 .. code-block:: none

    Ag+/Ag cathode, Cu anode (both reduction potentials): E = +0.46 V, spontaneous = True




.. GENERATED FROM PYTHON SOURCE LINES 29-31

The historical pitfall: taking the anode value from an oxidation-potential
table (sign flipped) and subtracting it gives nonsense.

.. GENERATED FROM PYTHON SOURCE LINES 31-34

.. code-block:: Python

    E_mixed = T["Ag+/Ag"].E_standard - (-T["Cu2+/Cu"].E_standard)
    print(f"Same cell with a mixed-convention anode value: E = {E_mixed:+.2f} V (wrong; measured 0.46 V)")





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

 .. code-block:: none

    Same cell with a mixed-convention anode value: E = +1.14 V (wrong; measured 0.46 V)




.. GENERATED FROM PYTHON SOURCE LINES 35-37

The whole table in both conventions: the oxidation-potential column is
the mirror image of the Stockholm (reduction) column.

.. GENERATED FROM PYTHON SOURCE LINES 37-53

.. code-block:: Python

    names = list(T)
    E_red = np.array([T[name].E_standard for name in names])
    order = np.argsort(E_red)
    y = np.arange(len(names))

    fig, ax = plt.subplots(figsize=(7, 7))
    ax.barh(y - 0.2, E_red[order], height=0.4, color="steelblue", label="Reduction potential (Stockholm, 1953)")
    ax.barh(y + 0.2, -E_red[order], height=0.4, color="lightgray", label="Oxidation potential (older convention)")
    ax.set_yticks(y)
    ax.set_yticklabels([names[i] for i in order], fontsize=8)
    ax.axvline(0.0, color="black", linewidth=0.8)
    ax.set_xlabel("Tabulated potential (V vs. SHE)")
    ax.set_title("One couple, two historical signs")
    ax.legend(fontsize=8, loc="lower right")
    fig.tight_layout()
    plt.show()



.. image-sg:: /api/gallery/electrochem/standard_potentials/images/sphx_glr_plot_02_stockholm_sign_convention_001.png
   :alt: One couple, two historical signs
   :srcset: /api/gallery/electrochem/standard_potentials/images/sphx_glr_plot_02_stockholm_sign_convention_001.png
   :class: sphx-glr-single-img






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

   **Total running time of the script:** (0 minutes 0.085 seconds)


.. _sphx_glr_download_api_gallery_electrochem_standard_potentials_plot_02_stockholm_sign_convention.py:

.. only:: html

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

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

      :download:`Download Jupyter notebook: plot_02_stockholm_sign_convention.ipynb <plot_02_stockholm_sign_convention.ipynb>`

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

      :download:`Download Python source code: plot_02_stockholm_sign_convention.py <plot_02_stockholm_sign_convention.py>`

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

      :download:`Download zipped: plot_02_stockholm_sign_convention.zip <plot_02_stockholm_sign_convention.zip>`


.. only:: html

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

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_