Of the three thermodynamic quantities, δg, δh, δs, which is most useful for determining spontaneity of a reaction?

Of the three thermodynamic quantities, δG, δH, δS.

δG is most important in determining spontaneity of a reaction as spontaneity of a reaction can be determined by its sign , when δG is negative, reaction is spontaneous and when δG is positive, reaction is non-spontaneous.

To check the spontaneity of a reaction , following reaction is considered:

δG= δH-TδS

Here,  

δG is gibbs free energy

δH is enthalpy change

δS is entropy change

T is the temperature

Based on the sign of δH and δS, δG sign can be determined that tells about the spontaneity of the reaction.

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.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).