Under what condition is phase rule applied

Under the equilibrium condition

Explanation:

according to the phase rule given by Willard Gibbs, under the condition where the equilibrium between the number of phases is not affected by the gravity, electricity magnetic force or by surface action and the system is under constant temperature, pressure and concentration then the degrees of freedom(F) is proportional to the concerntration (C) and the Phases(P) at equilibrium condition.  

the expression is given as : F= C-P+2

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

water at room temperature is flowing through a pipe with pressure taps located 10 ft apart along one section of the pipe, which are connected to a mercury (s=13.6) manometer.