Heat of Solvation

[ScatmanCrothers]

2 questions:

Does a high heat of solvation mean that the solvation is favorable or unfavorable?

Does a high heat of coordination (enthalpy of binding) mean the binding is favorable or unfavorable?

Context:

BR Ochem Ch. 8 Review Passage 3, question 17:

A large Rf value can be attributed to what factors?

C. High heat of solvation (deltaH of solvation) between the solute and solvent
D. High heat of coordination (deltaH of binding) between the solute and the silica gel.

My thinking:

A negative enthalpy means a process is favorable and gives off heat. A positive enthalpy means a process is unfavorable and requires heat. Thus, a "high heat of solvation/coordination" means that a lot of heat is required for the solvation/binding. This would mean that a solute with a high heat of solvation would not dissolve well in the solvent, and thus not travel far on the TLC plate. Conversely, a solute with a high heat of coordination would not bind well with the silica gel, and would travel far on the TLC plate.

So I chose D, but BR says the answer is C. Their reasoning is completely opposite of mine - that a high heat of solvation/coordination means the solute easily dissolves or binds. I have scoured the internet and all I can find is basic explanations that say a positive heat of solvation is endothermic, and a negative one is exothermic.

So confused here. Please help.

---

Members don't see this ad.

 

[ashtonjam]

I think 'high heat' is a poor way to describe enthalpy since the writers really mean the opposite. TBR uses that term to mean a very negative heat of enthalpy if I remember correctly.

 

[ScatmanCrothers]

I guess that would be the most probable explanation. So confusing though. Not sure which viewpoint I should take if I run into this on the actual MCAT.