A mixture is prepared by dissolving 0.200 mol NaCl(s) in water (ΔH = +3.9 kJ mol⁻¹)
CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A mixture is prepared by dissolving 0.200 mol NaCl(s) in water (ΔH = +3.9 kJ mol⁻¹). Silver nitrate solution is then added, precipitating AgCl(s) according to Ag⁺(aq) + Cl⁻(aq) → AgCl(s) with ΔH = –65 kJ mol⁻¹.
The total measured heat change for the combined sequence is –8.2 kJ.
Which statement best explains whether the overall process should be classified primarily as a physical or a chemical change?
(a) It is primarily a physical change because both steps involve solids changing state or phase, and no oxidation numbers change.
(b) It is primarily a physical change because the net heat released, 8.2kJ, is much smaller than typical chemical reaction energies.
(c) It is primarily a chemical change because most of the energy change comes from formation of Ag–Cl bonds during precipitation, which far outweighs the energy absorbed when NaCl dissolves.
(d) It is primarily a chemical change because dissolving NaCl breaks ionic bonds, making it the dominant chemical process in the sequence.