Physical Chemistry> about molar heat capacity...

when we put pressure constant molar heat capacity Cp.if the objects expand then it is less than Cv.when you subtract means Cp-Cv get negative sign.But R Universal gas constant value(which comes from the subtraction of those both two, ) become negative then how it is?

k bramhendra , 14 Years ago

Grade 11

2 Answers

SAGAR SINGH - IIT DELHI

Last Activity: 14 Years ago

Dear student,

Heat capacity (symbol C) is an extensive property , meaning it is a physical property that scales with the size of a physical system. A sample containing twice the amount of substance of another requires twice the amount of heat ( $Δ Q$ ) to achieve the same rise in temperature ( $Δ T$ ):

$C = \frac{\Delta Q}{\Delta T}$

ankitesh gupta

Last Activity: 13 Years ago

C_P AND C_VARE FIXED FOR MONOATOMIC, DIATOMIC ,POLYATOMIC MOLECULE SINCE CP AND CV ARE CALCULATED BE OBSERVING THEIR VIBRATIONAL MOTION , TRANSLATIONAL MOTION ETC. SO CP IS ALWAYS GREATER THAN CV AND IF YOU HAVE STUDIED FORMULA FOR ADIABATIC EXPANSION PV^GAMMA=CONSTANT WHERE GAMMA=CP/CV AND IF IN EXPANSION CV IS GREATER THAN CP THEN ACCORDING TO THE FORMULA THE FINAL VOLUME WOULD BE LESSER THAN THE INTIAL VOLUME BECAUSE CP/CV WOULD BE LESSER THAN 1 . BUT YOU HAD CONSIDERED THE PROCESS TO BE EXPANSION SO HOW COME VOLUME DECREASED THEREFORE YOUR ASSUMPTION WAS ONLY WRONG