Reversibility and properties of ammonium chloride reactions

Steps:

• Reaction 1 describes thermal decomposition of solid NH4Cl into NH3(g) and HCl(g), requiring heat input.
• Reaction 2 is the reverse: combination of NH3(g) and HCl(g) to reform solid NH4Cl, releasing heat.
• Evaluate choices: C provides the exact balanced equation for reaction 1.
• Eliminate A, B (incorrect energy types), and D (wrong on molecular structures).

Why C is correct:

• The equation NH4Cl → NH3 + HCl directly matches the products of heating solid ammonium chloride, per standard decomposition reaction.

Why the others are wrong:

• A: Reaction 1 absorbs heat (endothermic); reaction 2 releases heat (exothermic).
• B: Reaction 1 is endothermic; only reaction 2 is exothermic.
• D: NH4Cl has ionic lattice structure; only NH3 and HCl are simple molecular.

Final answer: C