Chem 101 1nd EditionExam # 1 Study Guide Lectures: 1 - 6Similar molar masses = induced dipole forces are about the same. Induced dipole forces increase with increasing molecular weight, so the boiling points of the straight chain alkanes increase as the number of carbon atoms in the chain increases. Therefore hexane, CH3CH2CH2CH2CH2CH3, has a higher boiling point than pentane, CH3CH2CH2CH2CH3.Dipole forces has a higher boiling point compared to nonpolar moleculesBoiling points increase as intermolecular attractive forces increase. For the alkanes, which are non-polar hydrocarbons, the intermolecular forces are induced dipole forces. In the case of the alcohols, the intermolecular forces include induced dipole forces, dipole forces, and hydrogen bonding.Hydrogen bonding causes a lower boiling pointHigher melting points are satisfied with a complete octetE represents the escape energy - the minimum kinetic energy that a molecule in the liquid must have in order to be able to break from the surface of the liquid and enter the gas phase. At higher temperatures, a larger fraction of the molecules in the liquid have enough energy to escape into the gas phase and the vapor pressure increases. When liquids evaporate, the molecules that escape into the vapor phase must have enough kinetic energy to overcome the intermolecular attractive forces. Increasing the temperature increases the number of molecules that have enough energy to escape into the vapor phaseand, therefore, increases the vapor pressure. The stronger the intermolecular attractive forces, the higher the temperature must be to achieve a certain vapor pressure.A liquid that must be raised to a higher temperature (when compared to another liquid) has stronger intermolecular forces.The liquid with the weakest intermolecular forces will have the highest vapor pressure at any temperatureThe heat of vaporization of a liquid is a measure of the energy required to overcome the attractive forces in the liquid. Therefore, the liquid with the stronger attractive forces would be predicted to have the highest heat of vaporization.Higher temperatures = stronger intermolecular forcesHigher temperatures = the larger the heat of vaporization V 1 x P1 = X mmHg If X mmHg > mmHg given then condensing occurs and liquid are presentV2V 1 x P1 = X mmHg If X mmHg < mmHg given then no condensing occurs and only vapor is V2 presentREMEMBER THAT ALL MATERIAL CAN BE TESTED ON THE FINAL. MAKE SURE TO REVIEW PREVIOUS STUDY GUIDES TO BE WELL
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