Question

Adding water to some chemicals can be dangerous because large amounts of heat are liberated. Which of the following does NOT liberate heat when water is added to it?

KNO3 (the answer)
NaOH
Na
CaO
H2SO4

I guessed Na simply because it's the only one that's an element, but this is just random and irrelevant "reasoning." How do I go about figuring out it's KNO3 and not the others?

Answer 1

Experience told me the answer. Lacking that you might be able to find a table that will tell you. See if you text has one on heat of solution or enthalpy of solution. Here is a partial table I found on the web.

Answer 2

Thanks for the table! It actually is in my text, but I am taking the AP test soon, so I won't have a table like that. I can only answer the question based on the periodic table and that's it. Is there anything else I can use to at least eliminate the other choices?