Instant heat packs and cold packs use compounds that have a negative or positive
ID: 574300 • Letter: I
Question
Instant heat packs and cold packs use compounds that have a negative or positive enthalpy of solution, AHsol, to produce a temperature change. The packs consist of a pouch of water and a dry chemical, CaCl2 for heat packs, or NH4NO3 for cold packs. The pack is activated by breaking the seal of the water pouch, which dissolves the dry chemical and forms a solution that either increases or decreases in temperature Predict the signs of AHsol and ASsol for the following solutions NH,NO3(s) H2O(1) NH,NO,(aq) ASsol > 0 AHsol 0Explanation / Answer
We know that Delta Hsolution = sum of Delta Hsol of products - Sum of Delta Hsol of reactants
Delta Ssol = sum of Delta S of gaseous or aqueous products- sum of Delta S of gaseous or aqueous reactants
1. Delta Hsol = 1-2= -1= - ve= <0
Delta Ssol = 1-0 = 1=+ve =>0
2. Delta Hsol = 1-2=-1 - ve=<0
Delta Ssol = 1-0=1 =+ve = >0