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Aatreya Chakravarti Ms. May April 22th, 2013 Chemistry Honors Comparing Rates of Evaporation Pre-Lab Questions

Chakravarti 1

2. What is evaporation? Describe what happens at the molecular level during evaporation. Evaporation is the process by which molecules undergo a change in state from a liquid to a gas. At a molecular level a molecule needs a set energy level to evaporate. When molecules collide they transfer energy. Eventually one molecule will get the energy required to change state and evaporate. This process is then repeated till another molecule is able to evaporate. Due to the high number of molecules present the rate of evaporation is faster than you can imagine. 3. List the three possible intermolecular forces. Which force is the weakest? Which force is the strongest? The first intermolecular force, the London Dispersion force, is the weakest of all the forces because it creates its bond for a very short time. The second strongest force, the Dipole-dipole force, is between polar molecules. The strongest of all intermolecular forces is the hydrogen bond which is between hydrogen and either oxygen, nitrogen or fluorine. 4. Look at the materials list for this lab. Consider the five liquids you will test. Predict which liquids will evaporate quickly and which will take longer to evaporate. Give reasons for your predictions. I predict that acetone, or C3H6O, will evaporate the quickest because there is no hydrogen bonds between oxygen and hydrogen. Therefore and London Dispersion bond is created which is very weak and doesn’t take much energy to break. The second liquid to evaporate will be isopropyl. C3H8O also like acetone doesn’t allow its oxygen to bond with any hydrogen therefore not creating hydrogen bonds. Also due to the polarity of isopropyl dipole-dipole bonds are created that aren’t very strong. The third liquid to evaporate will be ethanol due to its dipole-dipole force created by its polarity. H2O should obviously evaporate the quickest...
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