I admit I don't know chemistry (the science, not the code). So I can't determine what would be the best way to present this. I'm not sure that the tiny 2 above the 6 in the second equation is actually a replacement. The 6 is cancelled in 2 places which then wouldn't require a replacement. Also, the symbol before the H is a Greek cap delta. I will see if I can find someone to make sense of this.
I talked with someone who does know chemistry. By consensus we came up with this suggestion. I didn't concern myself with alignment of the addition problem. There is no alignment shown in print, and I'm not considering this a polynomial that would require alignment. I apologize about the replacement number -- that is what it is. Let me know what you think of this and whether it seems readable to you.
Hello. I would like to chime in about this problem. When you divide this spatial problem into vertical sections, you lose the connection between the cancelled terms. For example, it is not clear in the first portion (lines 6-9) why 6O2(g) becomes only one O2(g) because the 5O2(g) is to the right of the yields arrow. I suggest presenting this as three complete equations in a linear style (NIs needed). The reader will better be able to match the cancelled item if you do not break the equations apart. See attached braille file for an idea.