[davidenarb]

Let's consider the following raction aA+bB=cC+dD
it tells us that :   "a" mol of A contains "c" mol of C, but we write:
 c n(A) = a n(C)

I just find this is confusing with the sentence! for me : a n(A) = c n(C)

Thanks for the clarification

[discodermolide]

You have written an equation it is a chemical reaction where A + B goes to products C + D.
So what is your question?

[mjc123]

If n(A) = a and n(C) = c then c*n(A) = a*n(C) = ac, trivially.
For example, if a = 2 and c = 1, 2 moles of A (plus some B) react to give 1 mole of C (plus some D). Then the number of moles of A reacted is twice the number of moles of C produced, i.e. c*n(A) = a*n(C). Your preferred equation would give 4 = 1.