Sorry I have one other question that i'm unsure about. for the solution process of A (s)----> A (aq) the teacher demonstrates upon mixing A in H2O that the temp falls from 22 to 5 degrees C. The soluability of this solid is known to be 28g/100g H2O at 30 degrees C. If the solvent (water) temp is increased from 30 degrees C to 60 degrees C, we would expect the soluability of A to:

Question

a. decrease by 1/2
b. increase by 2X
c. not change
d.increase but we cannot determine the value w/o more info
e.decrease but we cannot determine the value w/o more info

i'm not sure how to solve this. any help is much appreciated

Answer 1

You can answer this with Le Chatelier's Principle. Let me write what happens in chemical form instead of words.
A(s) + H2O ==> A(aq) + cold OR
A(s) + H2O ==> A(aq) - heat. Isn't that what happens? I think so but check me out. Then we can rewrite this in more standard form as
A(s) + H2O + heat ==> A(aq).
Now, as we add heat, what happens to the reaction? It is shifted toward the right because heat drives it to the right. LeChatlier's Principle states that a system in equilibrium subjected to a stress will react in such a way so as to relieve the stress. Therefore, the system will move so as to remove heat and that means moving to the right because that uses up heat. That eliminates answers a, c, and e and leaves us ONLY with answers b and d. I would pick d because we don't have solubility data for more then the one temperature. I hope this helps but if you don't understand something about it, please repost but give exact details about what you don't understand.

Answer 2

this helped so much! thank you, i understand now.