Hi! Are Delta Hsolution and Delta Hreaction the same value in dissolution?

Question

Hi! Are Delta Hsolution and Delta Hreaction the same value in dissolution? Please help! I know qrxn and qsolution are opposite(signs). I'm confused as to if DeltaHsolution and DeltaHreaction are different.

Answer 1

Hello Chris, if I am understanding your question correctly, dissolution is not a chemical reaction.  Dissolution occurs when a solid, liquid, or gas is dissolved in a solvent to create a solution, making the substance of interest a solute.  This process, the heat of solution, consists of basically two steps.  When the substance of interest is an ionic salt, for example, energy is supplied to separate the ions (-lattice energy), and energy is evolved when the separated ions are surrounded by water (energy of hydration).  The difference between the negative lattice energy and the energy of hydration is the energy of solution (deltaH solution).  Note that no chemical reaction has transpired, but merely a phase change.

 

Hope this helps.