I think part of the issue is that the "Homework" close is being double-dipped as a "this question is too basic" close reason. (For the rest of this discussion, I exclude the obvious copy-and-pasted-from-a-book questions.)
People tend to bring "effort" up routinely with homework closes, but I think that's a bit of a red herring. Questions with a similar level of "effort" (or lack thereof) are posted, up-voted, and answered by Chemistry SE luminaries all the time, with nary a discussion of "homework". Effort per se doesn't factor into the key thing that's tipping these toward a "homework" close.
I'd say that the reason these types of questions get the homework close is that they're viewed as being too simplistic. People see the question and roll their eyes at the level of question. It's a question whose answer "should be obvious" to anyone with a moderate level of skill and knowledge at chemistry. The only people who would typically struggle with it are those who haven't successfully completed a typical High School/Undergraduate chemistry course. -- Which is why people reach for "homework": only people encountering this as a classroom exercise would be the ones who would bother to post it.
It's a trend I've seen in a number of these sorts of cases. Whether a question is viewed as "homework" or not depends on the perceived level of the question.
Have a question perceived as "advanced"/"difficult"? You probably don't need to post much background or evidence of "effort" in finding a solution. Simply state the problem and request an answer, and we'll trip over ourselves trying to answer it. -- That's the case even if the answer can actually be found in the go-to reference book for that sub-discipline. No recrimination about "not putting in sufficient effort" for not looking at the CRC handbook first ... provided the question sounds advanced.
In contrast, if you post a question whose answer "should be" obvious, you'll get hammered with "homework" close votes, and terse comments about "showing your effort" (as if adding "I looked at references A, B & C, and they didn't have anything to say about the topic" somehow improves the answer ...). -- If someone comes along and points out the answer actually isn't obvious at all, then suddenly everyone reverses track, rescinds the close votes, deletes the comments and up-votes the question for being thought-provoking, even without a substantial edits to the question.
I think that's the main issue with the (non-copy/paste) "homework" closes. The people doing the closing think the question is too basic (e.g. could be answered by your average undergraduate solely by consulting standard reference works). There's a general concern about questioners wasting answers' time and the whole "help vampire" thing, and people here (rightly) don't want to waste their time if a little more effort on the questioner's part could solve things. Basic questions are seen as wasting people's time, as the answer "should be" obvious. People then reach toward "homework" as the close reason, as the copy-paste-from-book style homework question is the purest expression of this "help vampire" issue, and the lack of a bright line on what constitutes "homework" questions lends itself to scope creep.
The solution to this is likely two-fold:
First, we have to decide (or re-confirm the decision) about the scope of the site. What sort of questions do we permit? Is Chemistry.SE only for professional-level chemistry questions, or chemistry questions at all levels? On the mathematics side, they have two sites, MathOverflow for the high-level professional Q&A, and Mathematics.SE, for people at all levels of interest. We don't necessarily have to split the site, but we should at least agree about what level of question is or is not appropriate for this site. (Are all chemistry related questions on-topic, or do you need a certain level of chemical sophistication in the question before it's on-topic?)
Secondly, once we have decided on a scope, we need to get people to stick with it. If we decide to rule out certain questions as being "too basic", we should make (and use) an off-topic close reason that's specific for the "too basic" reason. (No re-using the "homework" close.) We also need to make sure people know the limits to what the "homework" close is for (and not for).