general question: thermodynamics isothermal and adiabatic processes

[ihatebluescrubs]

hi guys,



For an isothermal process, heat passes freely and the temp remains constant. However, q=0 only in an adiabatic process. How can temp change be zero but have some q?

I’m having some trouble understanding that point in relation to adiabatic processes


Thanks!

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[indianjatt]

It's because Q+W = 0. Q = -W. in an isothermal process, there is no temperature change. As a result, the overall change in internal energy must be zero. If it wasn't, the energy of the system would increase/decrease, which would result in a change in temperature. However, this is avoided because the amount of energy which enters the system through heat is lost through work done by the system and the amount of energy lost by the system as heat is gained by the system through work done on the system. So there CAN be a change in q, but that must be accompanied by a -W value in order to not change the internal energy and thus the temperature.

 

[milski]

ΔU=Q+W

For an isothermal process ΔU=0 or Q=-W. In other words, whatever heat is added to the system is lost as work done by the system.

For an adiabatic process, Q=0 and all the changes in temperature are due to work being done on/by the system.

We don't talk much about processes which are both isothermal and adiabatic because when both Q and ΔU are 0 (isothermal and adiabatic), then W=0, or in other words nothing is happening.

 

[shaboobly]

temp change is 0 during phase changes. when you boil water, you must continue to add heat even at 100 C because you must think of temperature as the average kinetic energy of the molecules. during a phase change that kinetic energy must be passed throughout the sample so while heat is continuing to flow into the sample, it is just dispersing across the entire sample in order to change phase.