Question

Given that the data for neutralization of a weak acid $\left(HA\right)$ and strong acid with a strong base is:
$HA+O{H}^{-}\to A^{-}+H_{2}O;△H=-41.80kJ$
$H^{+}+O{H}^{-}\to H_{2}O;△H=-55.90kJ$
The enthalpy of dissociation of weak and would be:

• A. $-97.20KJ$
• B. $+97.70KJ$
• C. $-14.10KJ$
• D. $14.10KJ$

Answer 1

The correct option is A $-97.20KJ$

It is given that, heat of neutralization for a strong acid with a strong base is -55.90kJ.

Now, for a weak acid $HA$, some of this heat is consumed in completely dissociating the acid.

Hence,

$\Delta H_{\left(dissociation\right)}=\Delta H_{\left(HA\right)}-\Delta H_{(strongacid+strongbase)}$

$\Delta H_{\left(dissociation\right)}=-41.80-(-55.90)$

$\Delta H_{\left(dissociation\right)}=14.10kJ$