Kinetic Energy

[nothing123]

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Hi all,

If we have substance A with a heat capacity of 1 and substance B with a heat capacity of 2, then when both substances are raised from a temperature of 25 degrees to 50 degrees, then substance B has absorbed more heat. At 50 degrees now, is it true that substance B's kinetic energy is greater than substance A's? Or because since temperature is proportional to kinetic energy that they are the same? Does that extra heat that substance B absorbed go into potential energy then?

Thanks.

 

[AWhitehair]

Hi all,

If we have substance A with a heat capacity of 1 and substance B with a heat capacity of 2, then when both substances are raised from a temperature of 25 degrees to 50 degrees, then substance B has absorbed more heat. At 50 degrees now, is it true that substance B's kinetic energy is greater than substance A's? Or because since temperature is proportional to kinetic energy that they are the same? Does that extra heat that substance B absorbed go into potential energy then?

Thanks.

I think I understand what you are trying to get at here, and this is a good question. Let me see if I can work through this...

Because substance B has absorbed more heat (energy) than substance A, there will definitely be a difference in energy between the two substances somewhere. "Somewhere" can only be KE or PE, and since we know that the temp is the same for the two substances and KE is directly related to temp, we would assume that the difference would have to be in the PE of the substances. This is my guess. Anyone else?

 

[nothing123]

Hmm thanks, that does give me some reassurance. Basically, I encountered this problem in a book and it does say that substance B has more kinetic energy which struck me as odd. However, it is held widely that in thermodynamic terms, the internal energy is proportional to the temperature. Because of course when we add heat to a system, that goes into internal energy. The funny thing is that when we deal with gases, it is the kinetic energy explicitly that is proportional to temperature.

 

[kish180]

Hmm thanks, that does give me some reassurance. Basically, I encountered this problem in a book and it does say that substance B has more kinetic energy which struck me as odd. However, it is held widely that in thermodynamic terms, the internal energy is proportional to the temperature. Because of course when we add heat to a system, that goes into internal energy. The funny thing is that when we deal with gases, it is the kinetic energy explicitly that is proportional to temperature.

The previous poster was correct, the extra energy from the heat goes into PE, or more specifically, it goes into the increase in PE that results from molecules breaking into less ordered configurations (like from a solid to a liquid). The simplest example of this is the heat of fusion. When you add heat to a solid at its melting point, the temperature wont go up but the sample melts. Where does the heat go? ->into PE of the molecules because they are in a less stable and less ordered state.

 

[AWhitehair]

Hmm thanks, that does give me some reassurance. Basically, I encountered this problem in a book and it does say that substance B has more kinetic energy which struck me as odd. However, it is held widely that in thermodynamic terms, the internal energy is proportional to the temperature. Because of course when we add heat to a system, that goes into internal energy. The funny thing is that when we deal with gases, it is the kinetic energy explicitly that is proportional to temperature.

Really? What book is it? This confounds me.