[psychoNOT]

Acetone has a boiling point of ~56C.  Why does it evaporate at room temp (~20-25C) in seconds?  Concentrated ethanol also exhibits this behavior, with a bp of ~80C.  H2O obviously has a bp of 100C, and evaporates much slower.  Is this just because room temp is closer to the bp of acetone/ethanol than H2O?  Or does it also have to do with the fact that acetone cannot H-bond, and the extent of H-bonding with EtOH is insignificant as compared to H2O?

[Vidya]

Evaporation or low boiling points are due to weak intermolecular attractions.You are right that acetone has no H- bonding whereas ethanol has hydrogen bonding.Water has more stronger H bonding than ethanol.

[Honclbrif]

Because all liquids all have a vapor pressure. The boiling point is the temp when the vapor pressure equals the ambient pressure, but there are still molecules in the gas phase over the liquid before it reaches its boiling point. For some liquids (such as the ones cited), the vapor pressure is quite high, and consequently they evaporate rapidly.

[Vidya]

now vapor pressure is high because of low intermolecular forces of attractions .High vapor pressure means low boiling point also .

[orgopete]

The total pressure is the sum of the partial pressures, acetone and the atmosphere. If a compound is heated to its boiling point, then its vapor pressure can equal the system pressure.

If acetone is in a closed bottle, then an equilibrium will be formed so the vapor pressure and atmospheric pressure will reach an equilibrium. If the bottle is opened, then some of the acetone vapors will disperse and upset the equilibrium. As a result, more molecules can evaporate to balance the equilibrium. The evaporation takes energy from the liquid and the liquid temperature will fall. As a result, a new temperature and new equilibrium will attempt to form.

Acetone and ethanol evaporate because the vapors that form are being swept away. Compounds with high vapor pressures will evaporate more quickly in trying to maintain its equilibrium because more moles are in the vapor phase to be swept away.

[fledarmus]

There is also the fact that most air already has a moderate amount of water vapor present. On the Texas Gulf Coast, that amount is frequently close to 100% of the water the air can contain! I don't know of many places where the atmosphere is already saturated with acetone or ethanol. Well, occasionally frat parties might reach the alcohol saturation level...