Question

The absolute enthalpy of neutralisation of the reaction: MgO_(s)+2HCl_(aq) \(\rightarrow\) MgCl_2(aq)+H₂O (l) will be:

• A. less than - 57.33 kJ mol^-1
• B. - 57.33 kJ mol^-1
• C. greater than -57.33 kJ mol^-1
• D. 57.33 kJ mol^-1

Answer 1

The Correct Option is A

The enthalpy of neutralisation is the heat change that occurs when one mole of water is formed by the reaction of an acid with a base. The reaction provided in the question is:

\text{MgO}_{(s)} + 2\text{HCl}_{(aq)} \rightarrow \text{MgCl}_2_{(aq)} + \text{H}_2\text{O}_{(l)}

In this reaction, magnesium oxide (MgO) reacts with hydrochloric acid (HCl) to form magnesium chloride (MgCl₂) and water (H₂O).

For a typical acid-base neutralization reaction involving strong acids and bases, the enthalpy change is usually around -57.33 kJ mol^-1. However, MgO is a solid oxide, and its reaction with HCl involves not only neutralization but also the dissolution of MgO into MgCl₂ ions. This process requires additional energy, making the overall enthalpy change less negative.

Thus, for the given reaction of MgO with HCl, the absolute enthalpy of neutralization will be:

1. Less negative than the standard enthalpy of neutralization for strong acids and bases, which is -57.33 kJ mol^-1, because extra energy is needed for the dissolution of MgO.
2. The correct option is less than - 57.33 kJ mol^-1.

Hence, the reaction of MgO with HCl will have an enthalpy change less negative than -57.33 kJ mol^-1 because it is not a simple acid-base reaction but involves an additional dissolution process.