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Internal Energy

Posted: Sat Mar 14, 2020 6:21 pm
by Michael Du 1E
Can anyone please explain to me why when it is an isothermal reversible expansion, we can assume that internal energy is 0 and q = -w? Thank you

Re: Internal Energy

Posted: Sat Mar 14, 2020 6:27 pm
by Jiyoon_Hwang_2I
The internal energy is 0 because isothermal means the temperature is constant

Re: Internal Energy

Posted: Sat Mar 14, 2020 6:31 pm
by Venus_Hagan 2L
If the temperature is constant, there is no heat change and thus the change in internal energy is zero

Re: Internal Energy

Posted: Sat Mar 14, 2020 6:32 pm
by MinuChoi
The internal energy of an ideal gas is proportional to its mass and temperature (deltaU = 1.5*n*R*deltaT). Both mass and temperature are constant in an isothermal expansion, so the internal energy is constant (deltaU = 0).
Internal energy, heat, and work are related by deltaU = q + w. deltaU = 0, so q = -w

Re: Internal Energy

Posted: Sat Mar 14, 2020 6:33 pm
by Nawal Dandachi 1G
isothermal means that temperature is constant therefore internal energy would be 0

Re: Internal Energy

Posted: Sat Mar 14, 2020 6:36 pm
by Philip
Michael Du 1E wrote:Can anyone please explain to me why when it is an isothermal reversible expansion, we can assume that internal energy is 0 and q = -w? Thank you


Isothermal means the temperature is constant and so the internal energy doesn't change so the change is 0. If change in internal energy is 0 then 0 = q + w and so q = -w

Re: Internal Energy

Posted: Sat Mar 14, 2020 8:18 pm
by Hussain Chharawalla 1G
Temperature and internal energy are directly proportional. In a sense internal energy is a measure of temperature. If temperature is not changing, then internal energy is 0. If you are expanding then you must be inputting heat. If you are compressing then you must be releasing heat.