Gaming World Forums
General Category => General Talk => Topic started by: Marmot on November 22, 2008, 08:41:35 am
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hm, help.
I know how to get the final temperature but not the entropy change and this is due at 8 am!!!!! the asnwers are listed but dont know how to do the work for entropy.
You probably know that when two objects at different temperatures are brought into contact, heat always travels from the hotter object to the colder object; never the reverse.
Imagine that you have two copper blocks, one with a mass 300 g at a temperature of 26.9 oC, and another with a mass 268 g at a temperature of 133 oC. The two blocks are brought into contact with each other in an insulated container.
Specific heat of copper = 0.385 JK-1g-1
What is the sign of the entropy change for the heat transfer (enter positive or negative) that takes place?
Sign of entropy change = positive
What is the final temperature of the two copper blocks?
Final temperature = 77.0 oC
What is the entropy change for the heat transfer described in this question?
Entropy change = 2.50 JK-1
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i got some stuff I need to take care of over the during the next hour and gotta run for the moment, but I'll keep this page up and help ya out when i get back.
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ok thanks bud. idk, i generally dont have a problem even if i dont go to chem class with it because generally the questions are based from the info of the book and i just read it. but apparently the teacher got creative this week.. ive tried like a billion variations of the entropy formula for hours :(
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ok i know i have two find the dS for each of the blocks and add them. I tried the integral that gives nCqln(Tf/To) and added both and nuthin. i tried also dq(Tf^-1-To^-1) and nuthin either. fuck this
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honestly, I haven't done this stuff in years and I'm a little drunk right now, but I keep coming up with a different number for the entropy change.
I know that from thermodynamics rules, the change has gotta be positive because the copper is giving off heat and not drawing in heat from the surroundings.
I'll go dig through my books
nCqln(Tf/To)
that's what I was trying too
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i gotta go to bed man I'm falling asleep here, sorry i couldn't help much. good luck
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i solved dis
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how'd ya do it? I couldn't find my chem books
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this is a joke topic
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I'm pretty (read: very) drunk right now but don't you have to know the surface area of the sides that are touching of the two objects? TBH I don't study chemistry I study physics so I probably won't know about this.
I always wondered what entropy was though.
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What is the sign of the entropy change for the heat transfer (enter positive or negative) that takes place?
Sign of entropy change = positive
Oh man I suck at chemistry, but I do know that the sign would depend on which system you are looking at. If you're looking at the system of the first system, it'd be negative, since it's exothermic (giving energy to the other block). The change in enthalpy for the second system, however, would be positive, since it's endothermic (taking energy).
You should be able to use Hess's Law to figure out the equation by setting up your equations to get the reaction you need. The sum of the equation, after products/reactants appearing on both sides, should give you the equation that you need to use to find the change in enthalpy. Then, just determine the pathway you used, adding up the enthalpies (not forgetting negative enthalpies for equations you reversed).
I realize that this is probably already done with, but hopefully that helped. :/
Also, I got like a C+ (B- maybe if the curving is friendly!) in the class, so... :P
But I'm positive on the endo/exothermic thing.