answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.
according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.
δh(reaction) = ∑nδh(products) - ∑nδh(reactants)
δh(reaction) = [δh +δh] - [δh]
δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj
here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj
therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.