Question

based on the information in the table above, which liquid, cs₂(l) or ccl₄(l), has the higher equilibrium vapor pressure at 25°c, and why?
(a) cs₂(l), because it has stronger london dispersion forces
(b) cs₂(l), because it has weaker london dispersion forces
(c) ccl₄(l), because it has stronger london dispersion forces
(d) ccl₄(l), because it has weaker london dispersion forces

Explanation:

London dispersion forces increase with molar mass. \(CCl_4(l)\) has a higher molar mass (\(154\space g/mol\)) than \(CS_2(l)\) (\(76\space g/mol\)). Stronger London dispersion forces mean higher boiling point (since more energy is needed to overcome the forces) and lower equilibrium vapor pressure (as fewer molecules have enough energy to escape to the vapor phase). \(CS_2(l)\) has weaker London dispersion forces (lower molar - mass), so it has a higher equilibrium vapor pressure at \(25^{\circ}C\).

Answer:

B. \(CS_2(l)\), because it has weaker London dispersion forces