Physical Chemistry Chapter 7 The phase rule Two assumptions no chemical reactions occur (2)every chemical species is present in every phase Counting the total number of intensive variables .(properties that do not depend on the size of the system). The pressure P and temperature T count as 2 Specify the composition of a phase by giving the mole fractions of C-1 components( because x,+x2+... + c=1 and all mole fractions are known if all except one are specified. There are p phases, the total number of composition variables is plc-1). At this stage, the total number of intensive variables is p(c-1)+29 The Phase Rule Two assumptions: Counting the total number of intensive variables (properties that do not depend on the size of the system). The pressure P and temperature T count as 2. (1) no chemical reactions occur (2) every chemical species is present in every phase Specify the composition of a phase by giving the mole fractions of c-1 components (because x1+x2+…+xc=1, and all mole fractions are known if all except one are specified.) There are p phases, the total number of composition variables is p(c-1). At this stage, the total number of intensive variables is p(c-1)+2. Physical Chemistry Chapter 7