Why wouldn't you do this reaction directly in a lab (and would rather use Hess' Law to determine the enthalpy of formation)?:

Question

1/2N2(g) + 2H2(g)+ 1/2Cl2(g) -> NH4Cl(s)

I don't think the reactants are that dangerous...? It's still pretty safe to do in a lab, isn't it? Are they too dangerous?

Is it because they're all gases and it's hard to work with gases in a lab...?

Answer 1

Nitrogen does not readily react with hydrogen, you would have great difficulty driving this reaction to completion, in fact, NH4CL in a solid state is difficult to stabilize. Why is ammonium chloride used in fireworks?