Endothermic Decomposition Energy Diagram

Steps:

• Reverse the given exothermic formation reaction to get endothermic decomposition: NH₄Cl(s) → NH₃(g) + HCl(g), ΔH = +174 kJ mol⁻¹.
• In an energy diagram, reactants (NH₄Cl) start at lower energy level than products (gases).
• The pathway includes an activation energy barrier leading to higher product energy.
• Select diagram showing upward energy trend from reactant to products with a peak.

Why B is correct:

• Depicts reactants below products with activation energy hump, matching endothermic ΔH > 0 definition.

Why the others are wrong:

• A: Shows exothermic profile (products lower than reactants), reverse of decomposition.
• C: Lacks activation energy barrier, violating transition state theory.
• D: Inverts energy levels (products lower), incorrect for endothermic process.

Final answer: B