# Re: Enthalpy change in isothermal compression of ideal gas

*From*: "James Copeland" <chemcope@xxxxxxx>*Date*: Sat, 3 Sep 2005 18:24:09 -0500

<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.

.

**Follow-Ups**:**Re: Enthalpy change in isothermal compression of ideal gas***From:*James Copeland

**References**:**Enthalpy change in isothermal compression of ideal gas***From:*simondex

- Prev by Date:
**Re: Why the Universe Exists** - Next by Date:
**Re: If energy were not conserved** - Previous by thread:
**Re: Enthalpy change in isothermal compression of ideal gas** - Next by thread:
**Re: Enthalpy change in isothermal compression of ideal gas** - Index(es):