I'm not sure that your two examples are of the same species, or that they necessarily are both fallacies. Let's apply the principle of charity to interpretation, and see what happens.
Person A: "Why is 1 + 1 = 2?"
Person B: "Because if you collect one apple, and then collect another apple, 1 apple + 1 apple = 2 apples, so you now have 2 apples in total"
We could interpret example 1 as a Tarskian sentence:
S1 "1 + 1 = 2" is true if and only if 1 + 1 = 2.
S2 1 + 1 = 2 is an abstraction of saying putting a thing in a basket with another thing is the same as ending up with two things in a basket.
First, this isn't a temporally causal empirical relationship. It's a question of metaphysical consequence. In fact, it seems not only well reasoned, but true. Claiming that they both have a shallow syntactic similarity (1 x + 1x = 2x where x is either undefined or an object) and therefore is some form of circularity seems uncharitable. I think the only fallacy committed here is a false equivocation of statements, probably unintentionally.
Person A: Why do sodium and chloride ions react?
Person B: Because sodium chloride is formed.
This is a little more involuted. You have identified that chemical bonding occurs, dynamic equilibrium of bonding aside, reaction then product. As the other responses have noted, this provokes an intuition that suggests propter hoc and certainly doesn't serve as an adequate explanation. But, let's change the topic:
Person A: Why do men and women engage in romance?
Person B: Because marriages result.
Obviously, the logic applied to agents capable of apprehending consequence, it seems rather acceptable. So, romance occurs before marriage (at least in the Western world), but marriage often is a partial cause of romance. This is, in fact, what is called a teleological explanation, and would seem to be acceptable metaphysically for ionic compounds as a formal cause under Aristotle's four causes, which would have been controversial even in his time.
But all of that being said, it's definitely not propter hoc because it inverts the temporal order, not mistakes a cause on account of it. That inversion does make the second example, as far as I can tell, the fallacy of confusing cause and effect. The best way to tell is just invert the statements to see if they do work:
Person A: Why is sodium chloride is formed?
Person B: Because sodium and chloride ions react.
This then to me is strong confirmation that it is the fallacy that results from inverting cause and effect in reasoning; and while it's very thin on explanation (because it doesn't ground the chemical formation in VESPR theory), it does express a simple empirical consequence: namely, reactions contingently form products which is a true relationship between antecedent and consequence. Just don't conflate negligible explanation for fallacy. It's not.
So, the verdict is example 1 is a poor example that suffers from false equivocation, but the example 2 is a fallacy regarding cause and effect.