Which of the following statements about enthalpy of neutralization is correct? It

Step 1: Analyze the question We need to pick the true statement about enthalpy of neutralization, which is the heat change when an acid and a base react to form one mole of water.

Step 2: The concept

• For a strong acid and a strong base, both are fully ionized in solution. The reaction is essentially: H⁺(aq) + OH⁻(aq) → H₂O(l), ΔH ≈ −57 kJ/mol
• Because the net reaction is the same every time (HCl + NaOH, HNO₃ + KOH, and so on), the value is practically constant.
• For a weak acid or weak base, some energy is used to ionize the weak electrolyte completely, so the heat released is less (a smaller magnitude, for example about −52 kJ/mol for ethanoic acid + NaOH).

Step 3: Evaluate each option

• A. Constant for a strong acid and a strong base: Correct, as explained above (about −57.3 kJ/mol).
• B. Cannot be determined using a calorimeter: False. A simple calorimeter (such as a polystyrene cup) is the standard way to measure it.
• C. Has a positive value: False. Neutralization is exothermic, so ΔH is negative.
• D. Higher for a strong acid and a weak base: False. It is lower in magnitude, because energy is absorbed to ionize the weak base.

Step 4: Answer The correct option is A.

Tip: Remember "strong + strong = same heat, about −57 kJ/mol". Neutralization is always exothermic (negative ΔH), and weak acids or bases give a smaller magnitude because of the ionization energy needed.