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Hello,
I have a question on isobaric expansion (this is taken from the paper
published by Rozier and Viennot):
îAn ideal gas is heated at constant pressure. Its volume and temperature
both increase. Why?î
The question is quite easy to answer from the point of view of energy.
Heat transferred to the system is partially used to mechanical work (=
P*deltaV) and partially to increase kinetic energy of the molecules and
hence temperature.
But what happens in a molecular level? The molecules bounce from a piston
and exert a force on it. When temperature increases the molecules have
greater momentum which results to greater force in collisions. Increase in
volume decreases number of collisions per time unit. The overall effect is
that average force per area, pressure, remains constant.
Is there momentarily greater pressure exerted on the piston for instance
in the beginning of the process? A student of mine asked this and I
couldnít convince him that pressure is constant all the time (thatís why
it is called isobaric!). Have I given the correct argument or am I missing
something?
Regards,
Antti Savinainen
Kuopio Lyseo High School/IB
Finland