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How could we define homogeneous and heterogeneous surfaces (rigorously)?

It is among my exam questions (but I could not find any definition in my textbook or on the internet).

I would say the homogeneous surface is a surface made of one type of molecule (opposite of the heterogeneous surface). But my knowledge about surfaces is very surface (and I am surprised it is listed as an exam question) so are there any other conditions or is it enough?

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  • $\begingroup$ Homogeneous surface is not a thing at all. $\endgroup$ Sep 5, 2021 at 15:46
  • $\begingroup$ Why? Not even in an ideal case? $\endgroup$
    – user76255
    Sep 5, 2021 at 15:54
  • $\begingroup$ We talk of homogeneous mixtures and reactions when there is one phase and no surfaces at all. Otherwise we use the word heterogeneous. That's all. $\endgroup$ Sep 5, 2021 at 15:56
  • $\begingroup$ Yet it is literally one of the questions which my professor gave me $\endgroup$
    – user76255
    Sep 5, 2021 at 15:58
  • $\begingroup$ @IvanNeretin All depends on context. We can talk about homogenous/heterogenous surface in context of the surface itself, not the whole system. Like an object made of solid pure compound can have homogenous surface, but if made of a metallic alloy, it can have heterogenous surface, with properties location dependent. $\endgroup$
    – Poutnik
    Sep 6, 2021 at 8:09

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Homogeneous surface is the surface where we can (in the context of the scenario, like the purpose and required/available resolution and sensitivity) neglect any surface variability. Otherwise, the surface is heterogeneous.

It is important to say it is relative evaluation. For a set of surfaces, it can reach both extremes like "everything is homogeneous" to "everything is heterogeneous".

A visually homogeneous surface can be considered heterogeneous when evaluated by the enough zooming-in optical or electron microscope.

A visually heterogeneous surface can be considered homogeneous when evaluated from far enough or with low resolution or sensitivity for differences.

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