Question

Heat of neutralisation of an acid is the amount of heat evolved when one gram equivalent of the acid is neutralised by excess of the base. If true enter 1 else 0.

Answer 1

Hint: The Heat of Reaction (also known as Enthalpy of Reaction) is the change in the enthalpy of a chemical reaction that occurs at a constant pressure. It is a thermodynamic unit of measurement useful for calculating the amount of energy per mole either released or produced in a reaction. If the reaction in consideration is a neutralisation reaction then the heat of reaction will be called heat of neutralisation.

Complete answer:
When a reaction is carried out under standard conditions which are at the temperature of 298 K (25 degrees Celsius) and 1 atm of pressure and one mole of water is formed at the end of the reaction it is called the standard enthalpy of neutralization. It is regarded as a special case of the enthalpy of reaction. We define it as the energy released with the formation of 1 mole of water. A neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water as the product. The neutralization of a strong acid and strong base has a pH equal to 7 at the end of the reaction. The heat of neutralization is the amount of heat evolved when one gram equivalent of an acid is neutralized by one gram equivalent of a base in dilute solution.

For example,
Here, the heat of neutralisation is given by \[\Delta H=-13.7\text{ kcal}\] or\[-57\text{ KJ}\]. As we require one gram equivalent of acid and at least one gram equivalent of base for heat of neutralisation of an acid, the statement is true.

Note: For a reaction between a strong acid and a strong base the heat of neutralisation is fixed which is \[13.7\text{ kcal}\] but for weak acids or bases, the heat of neutralization is pH dependent. In the absence of any added mineral acid or alkali some heat is required for complete dissociation of the weak acid or base. The total heat evolved during neutralization will be smaller as some it got used up in dissociating the acid or base.