A question on thermodynamic and empirical temperature scales.. In a constant volume gas thermometer,the ratio of pressures is used to determine the ratio in temperatures.in the book: Sears, F.W. and Salinger G.I., “Thermodynamics, Kinetic Theory and Statistical Thermodynamics" the author states that this pressure is to be taken limiting.what is meaning and use of taking 'limiting' pressure?how can the limit be taken when the numerator is a constant and the denominator is a variable?

anyone who knows about this,please help!!

Question

A question on thermodynamic and empirical temperature scales.. In a constant volume gas thermometer,the ratio of pressures is used to determine the ratio in temperatures.in the book: Sears, F.W. and Salinger G.I., “Thermodynamics, Kinetic Theory and Statistical Thermodynamics" the author states that this pressure is to be taken limiting.what is meaning and use of taking 'limiting' pressure?how can the limit be taken when the numerator is a constant and the denominator is a variable?

anyone who knows about this,please help!!

unklerhaukus · Answer

do you have a formula i can look at?

unklerhaukus · Answer

it might have something to do with the fact that the temperature is only properly defined when it is stable, the limit might be the limit that time approaches infinity- ie the temperature/pressure has stabilized

anonymous · Answer

see this

unklerhaukus · Answer

do they mean the pressure is theoretically zero when the temperature is zero (cant actually happen)

anonymous · Answer

actually it says that we are using ratio of pressure of a gas at diff temp to find the ratio of the temperatures...and i dont know why it says to extrapolate the denominator pressure to zero to find the ratio...problem is that both pressures at ice and steam point are constants so how is their ratio not a constant but something to take a limiting value?

unklerhaukus · Answer

the termometer will take some time to stabilize

vincent-lyon.fr · Answer

I am not sure, but I think this remark is linked to the fact that the definition given in your book holds for an ideal gas.

An ideal gas does not exist: the 'ideal gas' is a model.

All gases are real, and properties will be matching the ideal gas model laws only when their (real) properties are extrapolated to 0 pressure.

anonymous · Answer

that is exactly what i initially thought too. but i dont know if the image is legible or not ; in the middle lines it says
"the pressure ratio is understood to be the limiting value extrapolated to zero pressure. "
the ratio taken is the ratio between pressures at steam and ice points.the problem is since these too are two constants then how is the ratio limiting...

i too think that the main intent of the limiting thing is to give the ideal gas behaviour to real gas but how exactly is it working...