CH4 and H2 O have about the same molecular weight. Which has the higher vapor pressure at room t

step 1 For this question, we are given two substances. The two substances are methane, CH4, and water.

CH4 and H2 O have about the same molecular weight. Which has...

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Key Concepts

Intermolecular Forces

Intermolecular forces are the attractions that exist between molecules, which determine many physical properties such as boiling point, melting point, and vapor pressure. Weaker intermolecular forces allow molecules to escape into the vapor phase more readily, leading to higher vapor pressure, while stronger forces, such as those found in polar or hydrogen-bonding liquids, lower vapor pressure.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid (or solid) phase at a given temperature. It is a measure of a substance’s tendency to evaporate; substances with higher vapor pressures at a given temperature tend to transition from liquid to vapor more easily due to weaker intermolecular attractions.

Hydrogen Bonding

Hydrogen bonding is a specific type of strong intermolecular force that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. This bonding significantly increases the cohesive forces in a substance, often resulting in lower vapor pressure because the molecules require more energy to escape into the gas phase.

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