HETEROGENEO US EQ UILIBRI UM 



239 



liquid at 0°C. is taken as zero or some other value. The entropy 

 of the vapor is greater than that of the liquid by the entropy 

 of vaporization, that is, the heat of vaporization divided by 

 the absolute temperature. In the case of the volume, only the 

 specific volume of the vapor is plotted, as that of the liquid 

 is so small that it cannot be shown on the scale of the dia- 

 gram. Let us now consider some actual values. 



so 



/OO /so 200 



T£Mf>e/fATUff£ /-V OeSRSES Cef^TJORADe 



Z50 



300 



Fig. 1. The specific entropy of liquid water and of saturated water 

 vapor, the specific volume of saturated water vapor, and the vapor 

 pressure of water, plotted against temperature. 



At zero degrees centigrade, if the entropy of the Hquid is zero, 

 that of the vapor is 2. 18 calories. The specific volume of water 

 vapor in equilibrium with liquid at zero degrees is 206 liters per 

 gram; it is evident that the volume of the liquid, 1 cc, is 

 negligible in comparison. In the equation 



dp 

 dt 



v" - V 



4}V «)i 



the terms must all be of the same kind; if the slope of the p-t 

 curve is given in atmospheres per degree, and the volume in 



