8. Here's another calorimetry problem to solve: A solid s cs ubstance with a mass of ty 200g is at its melting point temperature in a calorimeter. While the substance changes from a solid to a liquid at the same
temperature, the 400g mass of water in the calorimeter goes from an initial temperature of 80°C to a
final temperature of 30°C. (a) How much heat did the water lose while the substance melted? (b)
What is the heat of fusion of the substance that melted?
Your response here.

i know this one but can't get it

Explanation:

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.