as a start you have to learn what is represente with 2C and what with C2, wich dont exist (on the level of chemistry you are involved), as a help gasses (except nobel gasess), are in molecular shape ig N2,O2 ,and "other" compounds are in atomic state (there are few wich is important for you to know which are exceptions P4, S8...), and thuse are represented as ig: C, Ca, Pb, K, Na....
so 2C means two atoms of carbon, N2 means one molecule oh nytrogen (consisted of two atoms).
hope it helps
p.s. terms are used on the level of knowledge acorded to the question, formation of acetic acid is not the most educational (may get in several ways) in field of Hess law, it is more organic mechanisams.