`f_i^L = phi_i * P_i * "exp"{ v_i ( P - P_i )/(R* T )}`

Enter a value for all fields

Fugacity can be thought of as the activity of a gas.  This equation computes the pure component fugacity for the `i^(th)` a a multi-component mixture.

Often at system pressures close to atmospheric:  `f_i^L ~= P_i^"sat"`