12.2.4 - Enthalpy changes of neutralisation for strong and weak acids

Question 1

What is the standard enthalpy of neutralisation?

Answer 1

The enthalpy change at 100 KPa and a specified temperature, usually 298K when one mole of water is produced by the neutralisation of an acid with an alkali.

Question 2

Why is the nethalpy change of neutralisation similar for all strong bases with strong acids?

Answer 2

Both strong bases and acids are almost fully dissciated.

Question 3

What is the expected enthalpy change of neutralisation value for a strong acid and strong base?

Answer 3

-57.6 KJmol^-1

Question 4

For weak acids ethanoic acid and hydrogen cyanide, why is the value for the enthalpy change of neutralisation less exothermic?

Answer 4

Energy is required to fully dissociate the ions.
This process is endothermic so the overall value is less exothermic.

Question 5

The enthalpy change of neutralisation for the strong acid HF is more exothermic than the expected value (-57.6) why is this?

Answer 5

Ions need to be hydrated in solution which is an exothermic process. So the overall value is more negative.