A solution is prepared by dissolving solid ammonium nitrate, NH4NO3, in water. The initial temperature of the water was 25oC, but after the solid had dissolved, the temperature had fallen to 20oC. What conclusion may be made about delta H and delta S

ΔH is positive, ΔS is positive

Explanation:

The enthalpy of reaction (ΔH) is positive in an endothermic reaction. An endothermic reaction leads to a decrease in temperature. Hence the fact that the temperature was decreased from 25oC to 20oC shows that the reaction is endothermic therefore ΔH is positive.

Also, the equation of the dissolution is;

NH4NO3(s) > NH4^+(aq) + NO3^-(aq)

This means that the number of particles in solution were increased. The entropy increases with increase in number of particles hence ΔS is positive.

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.