Isothermal v. Adiabatic

[justadream]

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Isothermal: no change in temperature
Adiabatic: no change in heat



Under those two definitions, then in adiabatic conditions, you can change temperature.



And in isothermal conditions you can change heat? If so, what would this “change in heat” look like?

 

[derpina]

@justadream Imagine putting a fire under a closed system with a piston, the volume of the closed system goes up as heat goes through => all heat converts to PV work instantly. To keep temperature constant, this process has to be slow, but you don't need to worry about that detail for the MCAT.

Adiabatic, your system cannot receive energy in the form of heat.

 

[justadream]

@derpina

I'm still a bit confused.

So in isothermal, you can only change energy via work?

But in adiabatic, how does the temperature change from not gaining/receiving heat? Also from work?

 

[derpina]

@derpina

I'm still a bit confused.

So in isothermal, you can only change energy via work?

But in adiabatic, how does the temperature change from not gaining/receiving heat? Also from work?

No, you cannot only change via work. You can also lose the heat you gained to the environment.

The temperature change can occur from a reaction: endothermic reactions store energy in bonds, thereby reducing the available energy for kinetic/heat energy. Exothermic does the reverse, but the system has not received energy from the environment.

 

[Cawolf]

@derpina

I'm still a bit confused.

So in isothermal, you can only change energy via work?

But in adiabatic, how does the temperature change from not gaining/receiving heat? Also from work?

Technically temperature is proportional to energy. So an isothermal reaction results in no change in internal energy. All of the heat put in is used to do work. All of the work on the system is released as heat.

Adiabatic is defined as no transfer of heat. So the only way the internal energy can change is by doing work on/by the system.