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Chemistry: 2 samples of the same liquid but different temp  final temp? 
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#1
Nov108, 02:44 PM

P: 96

1. The problem statement, all variables and given/known data
75 mL of a pure liquid at 245 K is mixed with 100 mL of the same pure liquid 365 K. What is the final temperature? The answer is 314 K but I'm not sure why! Thank you! =) 2. Relevant equations It says this problem has to do with Calorimetry but I'm not sure why! Calorimentry equations involve q=mc(d)t...but how would you incorporate both liquids? 3. The attempt at a solution q=mc(d)t? I'm so lost, sorry! 


#2
Nov108, 05:32 PM

HW Helper
P: 1,542

Yes you need that equation. Energy is conserved. You need to remember that the heat lost by the water at 365 K is equal to the heat gained by the volume of water at 345 K.



#3
Nov108, 09:50 PM

P: 96

I'm sorry I'm afraid I still don't understand...how can I use q=mcat for this problem?



#4
Nov108, 10:18 PM

HW Helper
P: 1,542

Chemistry: 2 samples of the same liquid but different temp  final temp?
That equation tells you the amount of thermal energy that is transferred between a mass m and its surroundings to undergo a temperature change ∆T.
So, you have Q_{1} = m_{1}c∆T for the first volume of water, and Q_{2} = m_{2}c∆T for the second volume of water. When they are mixed, the heat lost by the water at the higher temperature will equal the heat gained by the water at the lower temperature. They will come to equilibrium at the final temperature, T_{f}. 


#5
Nov108, 11:13 PM

P: 96

But how can you set it up?
I tried mcat=mcat but you get 75=100 which is obviously not true..? Can you pleas explain how to solve the q=mcat problem? I'm really sorry I just don't get it... 


#6
Nov108, 11:47 PM

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P: 1,542

See if that helps. I can't say much more without just giving you the solution, so try to think through what I've said and see how far you can get. 


#7
Nov208, 07:57 AM

P: 96

Okay, thank you!!
I ended up getting 312.143 K which is a little off from 314. Did you guys get 314 or 312.1 like me? 75(Final245) + 100(Final365)=0 ("c" cancels) 75x 183675 + 100x  36500 = 0 (let "x" = temp final) 175x54625=0 x=312.143 


#8
Nov208, 09:12 AM

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#9
Nov208, 09:31 AM

P: 96

Opps, yes! A typo!
And I did get 313.6 when I tried it again. Thank you so much for your continued help and patience!! =) I really appreciate it because I know you didn't have to do it but you were willing to stick with me until I got it, which was really nice of you. Thanks again. 


#10
Nov208, 10:50 AM

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P: 1,542

You're welcome.



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