Internal Energy

$\Delta U=q+w$

Michael Du 1E
Posts: 117
Joined: Sun Sep 22, 2019 12:16 am

Internal Energy

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

Jiyoon_Hwang_2I
Posts: 101
Joined: Sat Sep 14, 2019 12:17 am

Re: Internal Energy

The internal energy is 0 because isothermal means the temperature is constant

Venus_Hagan 2L
Posts: 104
Joined: Fri Aug 02, 2019 12:16 am

Re: Internal Energy

If the temperature is constant, there is no heat change and thus the change in internal energy is zero

MinuChoi
Posts: 100
Joined: Wed Sep 18, 2019 12:15 am

Re: Internal Energy

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

Nawal Dandachi 1G
Posts: 102
Joined: Sat Sep 28, 2019 12:16 am

Re: Internal Energy

isothermal means that temperature is constant therefore internal energy would be 0

Philip
Posts: 100
Joined: Sat Sep 07, 2019 12:16 am

Re: Internal Energy

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

Hussain Chharawalla 1G
Posts: 100
Joined: Sat Jul 20, 2019 12:15 am

Re: Internal Energy

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.