Question

The magnitude of enthalpy of neutralisation of a weak acid is smaller than that of a strong acid. If true enter 1 else 0.

Answer 1

Hint : The enthalpy of neutralisation is the change in enthalpy when acid reacts with base forming water and salt.
A strong acid has more number of ${H^ + }$ ions to react with base than a weak acid which has less number.

Complete answer :
First, let us see what is enthalpy of neutralisation.
It may be defined as the change in enthalpy when one mole of acid is neutralized with one mole of a base forming water and salt.
The other thing that we should know is the difference between a weak acid and a strong acid.
A strong acid is the one that completely dissociates to give the ${H^ + }$ ions in the solution. There is 100 % dissociation.
While a weak acid is the one that does not dissociate completely that is 100 % but lesser than it. This means the number of ${H^ + }$ ions produced by a weak acid is less than the number of ${H^ + }$ ions produced by a strong acid.
Now, what happens in a neutralisation reaction is that
${H^ + } + O{H^ - } \to {H_2}O$
The change in enthalpy here is designated by $\Delta H$.
In case 1, when a strong acid combines with a strong base, it will give water and salt. Let the change in enthalpy ($\Delta H$) here be ‘x’.
Now in case 2 when a weak acid combines with the same base, then because the acid is weak, so less number of ${H^ + }$ ions will be available. Thus, the ${H^ + }$ ions will be the limiting factor here. So, with less number of ${H^ + }$ ions, less number of $O{H^ - }$ ions will combine.
Thus, the change in enthalpy ($\Delta H$) will be less.
Thus, the magnitude of enthalpy of neutralisation of a weak acid is lesser than that of a strong acid. So, this statement is true.

Hence, we will enter 1.

Note :
As magnitude is mentioned in the question then that means the value can be negative or positive. It will not matter. The sign does not matter if magnitude is mentioned.
The value of enthalpy of neutralisation is negative. If we consider even signs then the answer may change. Example- In general, the change in enthalpy for strong acid and strong base is around (-57 )$KJmo{l^{ - 1}}$ and for weak it comes out to be around say (-50) $KJmo{l^{ - 1}}$. If we see signs, the -50 is bigger than -57. So, considering only the magnitude here.