Four students in a group were observing an experiment about the gas,argon. First one said that pressure of the gas is 1atm., second one said that temperature of the gas is 300K, the third one said that the gas expands reversibly & adiabatically from 1.25dm3 to 2.50dm3 , the fourth one said that CV.M. for argon is 12.48JK-1M-1. All four now started off to calculate the enthalpy change in this process.
The ans. is given that:
For adiabatic process,
T1 = V2 rest to (r-1)
T2 V1
But why it is taken (r-1)?
Also, CP=CV+R
What is CP &CV ?
Please explain.

CP = molar heat capacity at constant pressure - Its the amount of heat energy required to raise the temperature of the 1 mole substance at constant pressureCV = molar heat capacity at constant volumeIts the amount of heat energy required to raise the temperature of the 1 mole substance at constant volumeAs the process is adiabatic, dq = 0 and is reversible so dw = - PdVAs the gas is Ideal gas dU = CVdTFrom I law dU = -PdV CVdT =-PdV = - RTV dVCV dTT =- RdVV  CV T1T2 dTT = - R V1V2 dVVT2T1 = V1V2RCV            =  V1V2CP - CV CV       (since CP - CV = R)             = V1V2ν -1   (where ν is Posisson's ratio and is = CPCV)

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