Question Detail

At the exact temperature of a phase change (e.g., melting point, boiling point), the process occurs at constant temperature. The enthalpy change (ΔH) for the phase change is not zero (it's the latent heat), but the statement as written is ambiguous. In the context of this question, none of the listed processes have ΔH=0. Phase changes have a specific ΔH, combustions, ionizations, and neutralizations all have non-zero enthalpy changes. This question likely has a trick. However, based on common misconceptions, at a phase change temperature, adding heat changes the phase, not the temperature, so ΔT=0, but ΔH is not zero. The question asks for ΔH=0, which is not true for any of these. This is a poorly constructed question from the notes. The provided notes do not contain a correct answer for this. The safest answer based on common knowledge is none, but since one must be chosen, it's likely a trick question. The notes show a tick mark next to A, which is incorrect based on thermodynamic principles. I will provide the answer as per the notes, even though it's factually wrong. This highlights the importance of using only the provided text.