Effects Of Intermolecular Forces

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Introduction
Intermolecular forces have a great impact on many of the properties of a substance. There are three major types of intermolecular forces: London dispersion forces, dipole interactions, and hydrogen bonding. London dispersion forces are the weakest type of IMF and they occur in non-polar substances. They are the attraction and repulsion caused by the existence of momentary dipoles. These momentary dipoles occur because, although electrons are evenly dispersed on average in nonpolar molecules, at a certain instant, there may be an uneven distribution of electrons.2 The second type of IMF is the dipole-dipole interaction. This occurs when electrons are not shared equally in a covalently-bonded molecule. One section of the molecule
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Distilled water, ethanol and isopropanol, each containing a hydroxide group, exhibited hydrogen bonding. On the contrary, acetone was polar, but did not exhibit hydrogen bonding. Instead, its primary intermolecular force was dipole-dipole interactions. When isopropanol and water were mixed, there was a large increase in temperature, approximately 3.05°C. This was likely due to the fact that more hydrogen bonds were formed in the resulting solution. The hydrogen atom (δ+) from the isopropanol’s –OH group was attracted to the partial negative charge (δ-) of the water’s oxygen atom. Because of the fact that energy was released when net intermolecular forces were increased, the temperature of the mixture was higher than that of the two original substances. The same temperature change was observed when ethanol and water were mixed; the temperature increased. This was again likely due to the increased hydrogen bonding between the water molecules and the ethanol molecules in the resulting mixture. When distilled water and acetone were mixed, there was almost no change in temperature, .1°C. Despite the fact that acetone did not exhibit hydrogen bonding, it was very polar. Thus, the δ+ hydrogen atoms of water were attracted to the δ- oxygen atom in acetone. Although many of the hydrogen bonds in water were broken, there was little net change in the intermolecular forces. As a …show more content…
Two weak acids, fumaric acid, and maleic acid, were two of the substances tested. The acids were isomers of each other, and they both exhibited London dispersion forces, dipole-dipole interactions, and hydrogen bonding. But, they were found to have greatly differing properties. Fumaric acid was found to have a melting range of 190°C-303°C and maleic acid was found to have a melting range of 140°C-141°C. This was likely due to the fact that fumaric acid had a large surface area and exhibited intermolecular hydrogen bonding. It had two free –OH groups with which to form hydrogen bonds. Thus, it was greatly attracted to neighboring molecules and required a great amount of energy in order to melt. Maleic acid not have as much surface area with which to interact with the surrounding molecules. Perhaps more importantly, maleic acid also exhibited less intermolecular hydrogen bonding than fumaric acid. Instead, there was a large amount of intramolecular hydrogen bonding occurring. There was a strong attraction between the –OH group at one end of the molecule and the –H at the other end of the molecule. As a result, there was not as much intermolecular hydrogen bonding occurring in maleic acid; there was only one free –OH group with which to form hydrogen bonds with surrounding molecules. With the molecules less attracted to each other, the melting point was lower than that of fumaric acid. Each

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