Understanding Internal Energy: Exploring the Role of Volume in Thermodynamics

[Amaelle]

Good day all !
I have a confusion regarding the use of the formula dU=CdT for computing internal energy for liquid or solid
like for instance in this exercice

We have an isothermal process so I thought that dU=0 so according to the first law of thermodynamics
dQ=-dW (we want to calulate the heat transfer)
but the solution was totally different, for them dU is different from 0 ! (they got the values of u1 and u2 from tables)

any hint would be highly appreciated thanks!

 

[Chestermiller]

Is there a change of phase?

 

[Amaelle]

thanks for your prompt reply
yes, i think we went from super heated zone to saturated liquide

 

[Chestermiller]

thanks for your prompt reply
yes, i think we went from super heated zone to saturated liquide

Is internal energy always just a function of temperature? Does internal energy change at constant temperature during a phase change?

 

[Amaelle]

Thanks a lot I got your point now!
because we are changing phase the temperature remains constant but still heat has been removed from the internal energy
internal energy does depend only on temperature when we are in the same phase.
thanks again!

 

[Apashanka]

Is internal energy always just a function of temperature? Does internal energy change at constant temperature during a phase chang

Isn't internal energy depends on volume also.??

 

[Chestermiller]

Isn't internal energy depends on volume also.??

That is taken into account in the steam tables, which the OP is using.