Which of the following indicates an exothermic heat of solution?

[V4viet]

Hey guys i need your help again thank you in advance for your time..

Which of the following indicates an exothermic heat of solution?
a) heat is evolved
b) the final solution is acidic
c) a precipitate is formed
d) the reaction is spontaneous

the answer is (A) however; after reading their explanation i understand a little bit..but i don't understand why it's no (C). I thought that when something is formed, it'll give off heat therefore it'll be an exothermic reaction. The only thing i can think of is that even if something precipitate.. it doesn't mean that it's stable..so when new bonds are formed but it's not stable than the old bonds then it wont give off heat..is this correct?
thanks for your time

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[Lshapley]

Hey guys i need your help again thank you in advance for your time..

Which of the following indicates an exothermic heat of solution?
a) heat is evolved
b) the final solution is acidic
c) a precipitate is formed
d) the reaction is spontaneous

the answer is (A) however; after reading their explanation i understand a little bit..but i don't understand why it's no (C). I thought that when something is formed, it'll give off heat therefore it'll be an exothermic reaction. The only thing i can think of is that even if something precipitate.. it doesn't mean that it's stable..so when new bonds are formed but it's not stable than the old bonds then it wont give off heat..is this correct?
thanks for your time

I think you are reading way too much into this problem. Don't look at the answers and come up with the answer first. What indicates an exothermic heat of solution? Exothermic means heat is produced by the reaction, and therefore the answer is (A), end of question and move on. You get in trouble on these MCAT problems if you don't answer the questions before you look at the answers (aside from glancing to see what type of answer they are looking for) before you make up your mind and then you sit there making up reasons why the rest could also be true. These other choices are designed to confuse you.

 

[Funky]

Hey guys i need your help again thank you in advance for your time..

Which of the following indicates an exothermic heat of solution?
a) heat is evolved
b) the final solution is acidic
c) a precipitate is formed
d) the reaction is spontaneous

the answer is (A) however; after reading their explanation i understand a little bit..but i don't understand why it's no (C). I thought that when something is formed, it'll give off heat therefore it'll be an exothermic reaction. The only thing i can think of is that even if something precipitate.. it doesn't mean that it's stable..so when new bonds are formed but it's not stable than the old bonds then it wont give off heat..is this correct?
thanks for your time

yes you are looking too into it. I'm sure there are some reactions that are endothermic when a precipitate is formed only because the heat of breaking the bonds is stronger than the heat of forming the precipitate like you said. But you can't argue that there is an endothermic reaction where heat is evolved. That simply does not make sense.

 

[Lshapley]

Right, remember you are looking for the "best" answer. Exothermic by definition means heat evolved. Any other answer is second best.

 

[V4viet]

THANK YOU SO MUCH GUYS..yeah i think that's my biggest prob w/ the MCAT..i get confused w/ the answers a lot..even when i know the answers myself..i should try your technique and keep it simple as possible..thanks again..gluck to everyone

 

[AlternateSome1]

You can make precipitate via endothermic reactions. The beaker winds up getting cold and you have to keep heating it to keep the thing going. It is kind of cool...frost can even form on the outside of the beaker.

 

[estairella]

You can make precipitate via endothermic reactions. The beaker winds up getting cold and you have to keep heating it to keep the thing going. It is kind of cool...frost can even form on the outside of the beaker.

That's what I came in to say too. Do not get exothermic confused with spontaneous.... that kinda stuff will only work in highschool.

Edit: Omg my 300th post. I should stop coming here...

 

[Funky]

That's what I came in to say too. Do not get exothermic confused with spontaneous.... that kinda stuff will only work in highschool.

Edit: Omg my 300th post. I should stop coming here...

300 is nothing!
check out the random thread. those guys have so much!