Why is the standard enthalpy of neutralisation for strong acids and bases similar?

The standard enthalpy of neutralisation for strong acids and bases is similar because they fully dissociate in water, releasing the same amount of energy.

In more detail, the standard enthalpy of neutralisation is the heat energy change when one mole of water is formed from the reaction of an acid and a base under standard conditions. For strong acids and bases, this process involves the complete ionisation of the acid and base in water. This means that they dissociate fully into their constituent ions. For example, hydrochloric acid (HCl) dissociates into hydrogen ions (H+) and chloride ions (Cl-), and sodium hydroxide (NaOH) dissociates into sodium ions (Na+) and hydroxide ions (OH-).

The reaction that occurs during neutralisation is the combination of H+ ions and OH- ions to form water (H2O). This reaction is exothermic, meaning it releases heat energy. The amount of energy released is the same for all strong acids and bases because the same reaction is taking place, regardless of the specific acid or base involved. This is why the standard enthalpy of neutralisation for strong acids and bases is similar.

It's important to note that this is not the case for weak acids and bases. These do not fully dissociate in water, meaning that not all of the acid or base is available to react and form water. As a result, the standard enthalpy of neutralisation for weak acids and bases is less exothermic (i.e., releases less heat energy) than for strong acids and bases.

In summary, the standard enthalpy of neutralisation for strong acids and bases is similar because they fully dissociate in water, allowing for the complete reaction of H+ and OH- ions to form water, which releases a consistent amount of heat energy.