Posted by eng on Monday, April 5, 2010 at 9:48pm.
sorry to repost this question but i'm confused on this part
The solubility of borax is directly proportional to temperature. Therefore, the sign of H is
A. negative
B. positive
C. unknown with the given information
like you said earlier, borax dissolves when heat is added, which is endothermic. But in this question, it doesnt tell you whether temperature is increasing or decreasing, so is the answer is C since it is unknown

chemistry(check my explanation)  DrBob222, Monday, April 5, 2010 at 11:08pm
I don't think the answer is c. Take a real scenario.
Assume the temperature is 10 degrees C. The problem clearly states that the solubility is directly proportional to T; therefore, it we increase the T to say 25 C, we KNOW we added heat and we KNOW it increases the solubility. Therefore, we write the equation as
borax(s) + H2O(l) + heat ==> borax(aq)
which makes delta H a positive number. I agree that the question doesn't state which direction the reaction is going but I interpret it as meaning in the direction for solution as opposed to in the direction for coming out of solution. I understand your point and you could be correct. But I don't interpret it that way. I guess the main reason I interpret it as I do is that when one talks about solubility we always seem to be interested in knowing how much of a certain solid will dissolve. Still, you could be correct.
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