What is the acentric factor and how is it used?

Acentric factor (omega) characterizes the non-sphericity of molecules, defined as: omega = -log10(P_sat/Pc) - 1 at T_r = 0.7. Simple fluids (Ar, Kr, Xe) have omega near 0; complex molecules have higher values (e.g., n-decane ~0.49). Uses: three-parameter corresponding states correlations (improve over two-parameter), alpha function in SRK and PR equations of state, Lee-Kesler correlation for compressibility, and property estimation methods. Higher omega indicates molecules with more complex structure or stronger polar interactions.