Question

Why would you expect the aqueous layer to become hot upon acidification with HCl? Explain clearly, using equations to further illustrate your answer

Answer 1

HCl will cause "heat of solution"

this is essentially, the heat evolved when HCl goes from concentrated HCl into diluted HCl

there is more H2O - HCl interactions

since these are not ideal, there will be release/absorbtion of energy

in the particular case of HCl, there will be release of energy

Recall that:

Step 1: solute breaks apart; this is Endothermic.

Step 2: solvent breaks apart. this is Endothermic.

Step 3: Solvent and Solute bond, this is Exothermic

Recall that

Hdissolution = H1 + H2 + (-H3)

Therefore, if H1+H2 > H3, this will be endothermic

If H1 + H2 < H3, this will exothermic process (the case of HCl)

If H1 + H2 = H3, this will be ideal solution