Thermodynamics

[saveourpens]

ok so the internal energy U of a system is equal to the sum of the kinetic and potential energies.

But according the the first law of thermodynamics, U can increase or decrease based on heat transfered into or out of the system and work done by or on the system.

I though that the sum of the kinetic and potential energies would remain constant, but that's obviously not the case.

I know I'm missing something here. Can someone please clear this up?

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[saveourpens]

never mind, when I look at it in terms of reactants and products it is pretty intuative that internal energy does changea

 

[LeonVCU]

Does anybody know why using a liquid with a lower heat capacity than water in a bomb calorimeter make it easier to study a reaction that generates only little heat?

 

[MD Odyssey]

Does anybody know why using a liquid with a lower heat capacity than water in a bomb calorimeter make it easier to study a reaction that generates only little heat?

If only a small amount of heat is released in the reaction, the temperature change could be very small and thus difficult to measure. I would imagine that using a liquid with a low heat capacity makes the change in temperature larger and easier to measure, which translates into a more accurate measurement of the heat evolved in the reaction.

 

[LeonVCU]

hmmm... Maybe q=MCAT. Since q is the same (small amount of heat released), as you decrease "c," you increase "T"

 

[MD Odyssey]

hmmm... Maybe q=MCAT. Since q is the same (small amount of heat released), as you decrease "c," you increase "T"

Yes. That is what I just said, although what is actually being measured is the change in temperature. So, if a particular experimental setup yielded a temperature change of 2 K, that would be difficult to measure. But, if it were done with a liquid having a lower heat capacity, then the temperature change could much larger and easier to measure.

Make sense?

 

[LeonVCU]

yep, thanks