Endothermic/Exothermic (Please help)

Label each of the following reactions as exothermic or endothermic ("exo" or "endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always thermodynamically unfavourable. There is no need to do any calculation, use chemical arguments to predict the sign of the enthalpy change.

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)


Cl2(aq) + 2 KBr(aq) → 2 KCl(aq) + Br2(aq)


N2(l) → N2(g)


NH3(g) + HCl(g) → NH4Cl(s)


S(s) + 3/2 O2(g) → SO3(g)

Pick from these > endo-by ,exo-none ,exo-by ,exo-on

Exothermic occurs when the state of the products is closer to the gaseous state than that of the reactants. Also, more gas molecules/compounds must be present on the product side.
Therefore,
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
N2(l) → N2(g)
Are Exothermic reactions.

Endothermic reactions occur when the state of the products is closer to the solid state than taht of the reactants. If there is a decrease in the number of gas particles from the reactants to the products, an endothjermic reaction has occured.
NH3(g) + HCl(g) → NH4Cl(s)
S(s) + 3/2 O2(g) → SO3(g)

I would say this has no change
Cl2(aq) + 2 KBr(aq) → 2 KCl(aq) + Br2(aq)