Reaction is : <span>2NH4Cl(s) + Ba(OH)2 x 8H2O(s)---->2NH3(aq)+BaCl2(aq)+10H2O(1) Delta H= 54.8kJ Molar mass of NH4Cl = 53.5 g/mol </span>(<span>23.7 g NH4Cl x (1 mol NH4Cl / 53.5 g NH4Cl) x (54.8 kJ / 2 mol NH4Cl) = 12.13 kJ</span>
First look at the stoichiometry of the reaction. The molar mass of NH4Cl is 53.5 gmol-1. There are two moles of it so we have 107g. If it takes 107g of ammonium chloride to absorb 54.8KJ of heat, we could relate this to the energy absorbed by 23.7g and obtain the result as shown in the image attached.