# Thermal physics

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Thread starter 4 years ago
#1
One mole of an ideal gas is contained within a cylinder by a frictionless piston and is initially at temperature T. The pressure of the gas is kept constant while it is heated and its volume doubles. If R is the molar gas constant, the work done by the gas is increasing its volume is

A) RT ln2
B) (1/2)RT
C) RT
D) (3/2)RT
E) 2RT

Why is the ans C?
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4 years ago
#2
(Original post by Cookieesss)
One mole of an ideal gas is contained within a cylinder by a frictionless piston and is initially at temperature T. The pressure of the gas is kept constant while it is heated and its volume doubles. If R is the molar gas constant, the work done by the gas is increasing its volume is

A) RT ln2
B) (1/2)RT
C) RT
D) (3/2)RT
E) 2RT

Why is the ans C?
Ideal gas law; (NB: Ideal gases are a fiction, they don't actually exist!) PV = nRT;

where P=pressure, V=volume, n=# moles, R=gas constant & T= temp... all in SI units.

Pressure remains constant, number of moles of gas remains constant, therefore; V=RT.

For the reason why the gas constant needs to be applied to temperature, and why the temperature system we use is hundreds of years out of date... well, read Four Laws that Drive the Universe, by Peter Atkins. Worked in the field a long time but never really understood it, until reading that little gem!
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