Re: Enthalpy change in isothermal compression of ideal gas




<simondex@xxxxxxxxx> wrote in message
news:1125710975.265005.211320@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Hi, Everyone!
>
> Is it true that isothermal compression of an ideal gas has zero
> enthalpy?
>
> Thank You Very Much.
>
> Truly Yours, Simon Dexter.

Yes. By definition: H = U = PV, and inherent in the definition of an ideal
gas is that its internal energy, U,depends only on temperature, T, and not
on its pressure, P, or volume, V. Also, for an ideal gas, PV = constant at
constant T (PV = nRT, and if T does not change, than neither does the
pressure-volume product, PV). An isothermal processs is by defintion one of
constant temperature, T. So, in general, deltaH = deltaU + delta(PV), and
since deltaU = 0 at constant T, and so does delta(PV), then deltaH (any
change in enthalpy, H) is necessarily zero for an ideal gas at a fixed T
whether or not its pressure (or volume) is changed.
Jim C.


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