Predicting products of chemical equations? Consider the equation $\ce{2 NaOH (aq) +Cl2 (g) —&gt; NaOCl (aq) + NaCl (aq) + H2O (l)}$. How would one know the products of this reaction? Is there a general way of doing this? I would have no earthly knowledge of predicting this. Is it that we would look at each molecule and decide which goes with which on the basis of octet? Also, why does it just so happen that 2 moles of $\ce{NaOH}$ react with 1 mole of chlorine? What would happen if it was a 1:1 ratio?
One would not "know" what the products of the reaction are, a priori. As mentioned by @IvanNerenten, the way you know is by studying chemistry. In fact, the reaction is different if you use cold NaOH vs hot NaOH. The reaction as written is with cold NaOH and is a disproportionation reaction.This is where the chlorine is both oxidized and reduced in the same reaction.