Vapor Pressure of Methanol

N. Poirier

Vapor Pressure of Liquids

1.) The vapor pressure of methanol increased as the temperature increased. The second graph showed a linear relationship between temperature and pressure of methanol. As the temperature increased more molecules have enough kinetic energy to overcome the intermolecular force of attraction between molecules in methanol.

2.) Methanol and ethanol have similar structures and similar intermolecular forces however Ethanol is a heavier molecule than methanol. The difference in molecular mass means stronger London dispersion forces in ethanol which in turn translates into a lower vapor pressure. The calculated vapor pressures for methanol and ethanol don’t support this, because methanol’s vapor pressure is -2.18 kPa and ethanol’s is 7.91 kPa. Fortunately the parameters for methanol’s pressure cannot be a negative value, which allows me to conclude that the measured pressure at room temperature for methanol and (or) the air pressure was recorded incorrectly.

3.) Trial 1 was done at room temperature. Trials 2-6 must be calculated because the temperature was changed. When we changed the flask to a warmer temperature bath the air in the flask exerted pressure. The variation of pressure inside the flask must be taken into account and calculated.

4.) The purpose of the experiment was to see that temperature and vapor pressure have a direct relationship to each other meaning when one increases so does the other. The data we recorded and calculated supports this idea. As the vapor pressure went up so did the temperature. Increasing the temperature the kinetic energy increases the rate at which collisions occur. This increase in kinetic energy allows the methanol to evaporate faster, because converting a liquid to vapor involves overcoming the forces between the molecules in the liquid. The experiment also showed that methanol and ethanol have different intermolecular forces, thus different vapor pressures.

5.) The...