Evaporation and Intermolecular Attractions

Pre-lab:

Data:

Questions:

2) Explain the differences in the difference in temperature of these substances as they evaporated. Explain the results in terms of intermolecular forces.

Temperature change is directly related to the evaporation rate. This is because a substance gets energy from its surroundings to evaporate in the form of heat, so its surroundings get colder. The difference in temperature of the substances increases from lowest to highest in the following order: glycerin, n-Butanol, water, ethanal, methanol. All the substances have hydrogen bonds, but have different masses and different hydrogen bonding ratios, which cause these differences in temperature. Higher mass and more hydrogen bonds increase intermolecular force. Glycerin has the highest mass and contains many hydrogen bonds, and its change in temperature is lowest. (Also, Glycerin's temperature increases because it actually solidifies, due to its many hydrogen bonds and large mass, and discharges energy to its surroundings.) N-Butanol has a mass less than glycerin but greater than the other substances, and therefore has the next highest change in temperature. Although water has a low mass, both bonds between its atoms are hydrogen bonds, which are the strongest. Thus, its low mass and high hydrogen bond ratio balanced each other out, causing water to have an intermediate change in temperature. Ethanol has a higher mass than the previous substances, so a higher change in temperature. Finally, methanol has the highest mass and also the highest change in temperature.

3) Explain the difference in evaporation of any two compounds that have similar molar masses. Explain your results in terms of intermolecular forces.

When methanol, ethanol, and n-Butanol are compared, their individual masses need to be taken into consideration. When particles of a substance have a high masses,  the intermolecular forces increase and the substance takes a longer time to evaporate. Methanol has a high evaporation rate due to its low mass. Ethanol has the next highest evaporation rate due to its mass being in between the other two substances. N-Butanol has the lowest evaporation rate because it has the highest mass.

4) Explain how the number of —OH groups in the substances tested affects the ability of the tested compounds to evaporate. Explain your results in terms of intermolecular forces.

The number of —OH groups in the substances slows the evaporation rates of the substances. This is due to the fact that hydrogen bonding is relatively strong. Hydrogen bonding increases intermolecular forces by keeping the molecules of the substances close together.