The situation obtained when a perfect gas expands into a vacuum is
- ĪH is positive and TĪ S is zero
- ĪH is positive and T Ī S is negative
- ĪH is negative and TĪ S is zero
-
ĪH is zero and T Ī S is positive
The correct answer is: D
Explanation
The definition of enthalpy change is
ĪH = ĪU + Pex(ĪV)
The enthalpy change is zero because both terms on the right are zero in free expansion of an ideal gas.
There is no external pressure in a free expansion, so P (ex) = 0. And the internal energy change, ĪU of free expansion in a closed system is zero since no inter molecular forces have to be overcome. The temperature remains constant and no heat is absorbed or released.
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