Briefly explain when is it more adequate to use to use enthalpy H and when is it more

adequate to use internal energy U when applying the first law.

We consider an insulated piston$-$cylinder system $($with piston free to move$)$ that contains $2$L of

saturated liquid water at pressure of $250$ kPa $.$ Water is being heated with a $0\mathrm{.}5$ Omega$-$resistor at $12$ V

for a certain amount of time Delta t$,$ after which $10\%$ of water has evaporated.

Show that the change of specific enthalpy $($ic$,$ enthalpy per unit of mass$)$ during this process

is xh$\_($fg$)($with x the quality at the end of the process$).$

Using the first law, find the duration Delta t during which the electric circuit was tuned on$.$

Now assume instead that the piston is fixed, find the new value of Delta t$.$

Can you explain in simple words $($without needing to do any computation$)$ why you should

have expected that the duration you found in $4$ to be shorter than that in $3.($Hint: Where does

the electric work go in each case?$)$

DO NOT USE CHATGPT please