Which statement concerning the vapor pressures of water and methanol (CH3OH) is

Question

Which statement concerning the vapor pressures of water and methanol (CH3OH) is true?

At 25ºC, methanol has a higher vapor pressure than water because methanol has a lower normal boiling point than water.

At 25ºC, methanol has a higher vapor pressure than water because methanol is a poorer solvent than water.

At 25ºC, methanol has a higher vapor pressure than water because methanol is a less viscous liquid than water.

At 25ºC, methanol has a higher vapor pressure than water because the density of methanol is less than the density of water.

At 25ºC, methanol has a higher vapor pressure than water because methanol has weaker intermolecular forces than water.

Explanation / Answer

Methanol has weaker intermolecular forces compared to intermolecular forces in water. Due to the weak intermolecular forces, the energy threshold is lower as a result of which a large number of molecules (a large fraction of molecules to be precise) can easily overcome their forces. Due to this at any temperature, methanol has more number of molecules in the gas phase leading to higher vapor pressure.

So, at 25oC, methanol has a higher vapor pressure than water because methanol has weaker intermolecular forces than water.

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