I just came across this in one of the example sentences and was wondering the difference between these two verbs. Bear in mind, example sentence used します so is it just a polite way of saying it?
They are different in a few ways. 代用 includes the “substitution” aspect but also the “use” aspect in 用. So it’s both actions in one… changing to something else and then using that thing.
代わる is just a general word for substituting.
代用する is transitive, and basically it’s always going to be used in a scenario where some person is substituting one thing for another thing.
Additionally, kanji compounds are often “heavier” words than their counterparts. They are more likely to be used in writing or formal situations.
あるものを代用する and あるものに代えて、別のものを用いる basically mean the same thing, but one uses the kanji compound, the other uses verbs of Japanese origin.
代わる is intransitive, so the substituting thing is the subject itself, not some other agent.
If any of that still isn’t clear, let me know.
Yes, します is the polite form of する.