Answer to Question #16143 in Physical Chemistry for sara

Question

I dissolved two different white solids into water. One solid dissolved and gave off heat and the other became cold. Reading various texts online, I was not sure if these were physical or chemical changes. Some texts say if these solids are salts then these are physical changes. Other texts say since ionic bonds are broken, these are chemical changes. Which one is correct?

Answer 1

Both of them are correct,because you don't now what kind of compounds are this
white solid. In the case of NaOH or Ca(OH)2 or KOH it is physical changes,cause
water "destroys bond" between Me^x+ and xOH^. The same with kind of salts
Mex(A)y <---> xMe^y+ + yA^x- ,but in the case with alkali solid become
hot,and with salts in can become cold or hot.
But in the case,when white
solid is Na2O or CaO or other white solid oxide of some active metals it's
chemical changes
Na2O + H2O -->2NaOH and this reaction produced heat.