Answer
$-56.07\ kJ/mol$
Work Step by Step
From the definition of heat capacity:
$(100.0+50.0)\ mL\times 1.00\ g/mL\times 4.2\ J/g.K\times (24.28-22.50)\ K=1121.4\ J$
Exothermic reaction since the temperature increases.
Number of moles of CsOH:
$0.200\ M\times 100\ mL=20\ mmol$
Number of moles of HCl:
$0.400\ M\times 50\ mL=20\ mmol$
Both reactants are in stoichiometric proportions.
Enthalpy per mole:
$-1121.4\ J\div 20\ mmol=-56.07\ kJ/mol$
