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    				| 1. | 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» (–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 | |