Q1(d). Components in ammonium chloride dissociation

Answer in brief

For NH₄Cl(s) ⇌ NH₃(g) + HCl(g), the general reacting system has two components; equal ammonia and hydrogen chloride amounts impose an extra composition constraint, reducing it to one component.

Key points

• There are three chemical species and one independent reaction, so without further restriction C = S − R = 3 − 1 = 2.
• Starting from pure ammonium chloride, or equivalent NH₃ and HCl, dissociation produces the gases in a 1:1 ratio: p(NH₃) = p(HCl).
• This is one additional independent restriction. The constrained component count is C = 3 − 1 − 1 = 1.
• Adding excess NH₃ or HCl removes the equal-partial-pressure condition; only Kₚ = p(NH₃)p(HCl) is fixed, so the gas ratio can vary.
• Two independent components, for example NH₄Cl and NH₃, are then needed, giving C = 2.