Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
Subject: Re: isobaric expansion
Date: Fri, 17 Mar 2000 10:00:16 -0800
From: Leigh Palmer <palmer@SFU.CA>
At 9:05 AM -0800 3/17/00, Savinainen Antti wrote:
Hello,paper
I have a question on isobaric expansion (this is taken from the
published by Rozier and Viennot):temperature
îAn ideal gas is heated at constant pressure. Its volume and
both increase. Why?îenergy.
The question is quite easy to answer from the point of view of
Heat transferred to the system is partially used to mechanical work(=
P*deltaV) and partially to increase kinetic energy of the moleculesand
hence temperature.piston
But what happens in a molecular level? The molecules bounce from a
and exert a force on it. When temperature increases the moleculeshave
greater momentum which results to greater force in collisions.Increase in
volume decreases number of collisions per time unit. The overalleffect is
that average force per area, pressure, remains constant.instance
Is there momentarily greater pressure exerted on the piston for
in the beginning of the process? A student of mine asked this and I(thatís why
couldnít convince him that pressure is constant all the time
it is called isobaric!). Have I given the correct argument or am Imissing
something?
Regards,
Antti Savinainen
Kuopio Lyseo High School/IB
Finland
If you consider the details of the process then the pressure must
differ
any time the piston is accelerating. Your explanation (which is very
clear
and should be understood by any student) pertains to equilibrium
states
through which the system passes during the process of isobaric
expansion
or, alternatively, to comparison of two static equilibrium states.
If the
piston is accelerating then clearly thermodynamic equilibrium does
not
describe the system.
Leigh