Some Problems on the Value of Cp -Cv for Liquids and Solids
Li Ruxiong (Chemical Engineering Department)
A systematical discussion on Cp -Cv value for liquids and solids is presented in the paper. It is general that the Cp-Cv value for organic liquids reaches up to 5R. The average value of (Cp - Cv)/Cp for solids also reaches up to 4%. Therefore Cp - Cv≈0 is not right. This is because the increase of the internal potential energy of liquids and solids is larger during the expansion at constant pressure. In practical application,the capacity of co-exist phase must be used .because there must be space above the liquids, as well as pores in the solids or gaps between solids and containers. The capacity of liquids or solids equilibrated with vapor is very close to Cp. Hence only Cp of liquids and solids instead of Cv is used even in the isochoric process.
【CateGory Index】： O642