Question

Equal volumes of methanoic acid and sodium hydroxide are mixed. If $x$ kJ/mol is the heat of formation of water, the heat evolved (in kJ/mol) on neutralisation will be:

• A. more than $x$
• B. equal to $x$
• C. twice of $x$
• D. less than $x$

Answer 1

The correct option is D less than $x$

Methanoic acid is a weak acid and therefore, energy will be required for its dissociation. Thus, the energy released on neutralisation of methanoic acid and sodium hydroxide giving salt and water will be less than the heat evolved during the formation of water.

Hence, the heat evolved on neutralisation will be less than $x$.