Which of the following is correct for free expansion of ideal gas under isothermal condition :-

Explanation

For isothermal (T = constant) expansion of an ideal gas into vacuum, `w=0` since `p_(ex) = 0`. Also, Joule determined experimentally that `q=0`, therefore, `Delta U=0`
`Delta U= q+w` can be expressed for isothermal irreversible and reversible changes as follows:
1. For isothermal irreversible change
`q=- w = p_(ex) (V_(f) - V_(i) )`
2. For isothermal reversible change
`q=-w = nRT "ln" (V_f)/( V_i) = -2.303 nRT log "" (V_f)/( V_i)`
3. For adiabatic change, `q=0`
`sigma Delta U= W_("ad")`