While performing a thermodynamics experiment, a student made the following observations.

HCl + NaOH $\to$ NaCl + H₂O $\Delta$H = $-$57.3 kJ mol^$-$1

CH₃COOH + NaOH $\to$ CH₃COONa + H₂O $\Delta$H = $-$55.3 kJ mol^$-$1

The enthalpy of ionization of CH₃COOH as calculated by the student is _____________ kJ mol^$-$1. (nearest integer)