ABSTRACT
When solving a problem of phase or chemical equilibrium, it is necessary to know if there is enough information or it would be necessary to specify some variables before evaluating the remaining variables. As in any multivariable system of equations, if the number of variables is equal to the number of independent equations, the system can be solved. If there are more equations than variables, the system is overdetermined and, in the general case, no solution exists. On the other hand, if there are fewer relations than variables, the system is underdefined. The difference between the number of variables and the number of relations between them gives the available degrees of freedom (DF), that is, the number of variables that need to be specified in order to solve for all others.
