Physical Chemistry Chapter 7 The phase rule The difference between(a) constituent and(b) component constituent: a chemical species(an ion or a molecule that is present in a system component: a chemically independent constituent of a system number of components(c: the minimum number of independent species necessary to define the composition of all the phase present in the system4 The Phase Rule The difference between (a) constituent and (b) component constituent: a chemical species (an ion or a molecule) that is present in a system component: a chemically independent constituent of a system number of components (c): the minimum number of independent species necessary to define the composition of all the phase present in the system Physical Chemistry Chapter 7