Question

Expansion of a gas in vacuum is called free expansion. Calculate the work done and the change in internal energy when 1 litre of ideal gas expands isothermally into vacuum until its total volume is 5 litre?

Answer 1

“First law of thermodynamics”:

According to this law, the change in “internal energy” of a closed system will be equal to the energy added to the system minus the “work done” on its “surroundings” by the system.

$\Delta { E }_{ int }\quad =\quad Q\quad -\quad W$

This is the law of conservation of energy written in a form useful to systems involving heat transfer.

$(-w)\quad =\quad { p }_{ ext }({ V }_{ 2 }-{ V }_{ 1 })$

$=\quad 0\quad \times \quad (5-1)\quad$

$(-w)\quad =\quad 0$

According to first law of Thermodynamics,

$q\quad =\quad \Delta U\quad +\quad (-w)$

$0\quad =\quad \Delta U\quad +\quad 0$

Therefore, $\Delta U\quad =\quad 0$

Answer 2

Answer:

Answer is Zero

Explanation:

(–w) = pext (V2–V1) = 0 × (5 – 1) = 0 For isothermal expansion q = 0 By first law of thermodynamics q = ΔU + (–w) ⇒ 0 = ΔU + 0 so ΔU = 0