The enthalpy change for the neutralization of a weak acid with sodium hydroxide is smaller than that for a strong acid. This is because the weak acid does not completely dissociate in water, so there are fewer H+ ions available to react with the hydroxide ions. As a result, the reaction does not produce as much heat.

Comparison of heat flow for neutralization of weak and strong acids

The following table compares the heat flow for the neutralization of a weak acid (acetic acid) and a strong acid (hydrochloric acid) with sodium hydroxide:

| Acid | Enthalpy change (kJ/mol) |

|---|---|

| Acetic acid | -56.2 |

| Hydrochloric acid | -57.3 |

As can be seen from the table, the enthalpy change for the neutralization of acetic acid is smaller than that for hydrochloric acid. This is because acetic acid is a weak acid and does not completely dissociate in water.

Conclusion

The heat flow for the neutralization of a weak acid with sodium hydroxide is smaller than that for a strong acid because the weak acid does not completely dissociate in water. This results in fewer H+ ions available to react with the hydroxide ions, which in turn produces less heat.