$5.$ The $\_$ coefficient is a dimensionless quantity that reflects how much a substance's fugacity deviates from its pressure.

$6.$ In phase equilibrium, the fugacity of each component in the liquid phase must equal its fugacity in the $\_$ phase.

$7.$ The $\_$ Equation is a graphical method used to estimate the fugacity coefficient of a substance.

$8.$ The Van Laar equation is another model used to estimate activity coefficients, focusing on $\_$ binary systems.