SCAN0045 - V—r uw 7‘ W'j a ”V— e a if Chapter 12...

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Unformatted text preview: V—r uw 7‘; W ., . 'j a. / ”V— e , ' - a. ' if /// Chapter 12 Questions about Intermolecular Forces a. Explain why AsH3 has a higher BP at -62°C compared to GeH4 which has a BP of —90"C. AsH3 is polar with dipole-dipole interaction While GeH4 is non—polar with London Forces. Since Dipole-Dipole Interactions are stronger, the boiling point for AsH3 will be greater. b. Explain Why methane has a BP of -164°C and hexane has a BP of 69°C. Methane and hexane are both non-polar and only have London Forces. The difference is the molecular weight. Since hexane has a much higher molecular weight than methane, it’s electrons are more polarizable and thus the London Forces will be stronger for hexane compared to those in methane. The stronger forces will make the boiling point higher for hexane. 0. Explain why 2,2—dimethylpropane (BP 95°C) and pentane (BP 361°C), both having the same MW have different BP. The 2,2-dimethylpropane has a smaller surface area compared to pentane. Both are nonpolar with only London Forces and both have the same molecular weight. Thus, it is only that fact that pentane has the larger surface area, thus the electrons would be more polarizable for pentane compared to 2,2—dimethylpropane and thus contributes to the higher boiling point. d. Explain why ethanol has a BP of 783°C whereas ether (CH3—O—CH3) (same MW as ethanol) has a BP of -24.8°C. Ethanol has hydrogen bonding and ether had dipole—dipole interactions. They are both polar but the hydrogen bonding has a stronger interaction and thus the boiling point of ethanol is higher than ether. e. Explain Why the BP of CH4 is less than SiH4 but the BP of NH; is greater than PH3. Ammonia has hydrogen bonding whereas phosphine only has dipole—dipole interactions. Since the hydrogen bonding interaction is stronger than dipole-dipole, the boiling point for ammonia is higher than that of phosphine. For methane and silane, the molecular weight and thus the polarizability is greater for silane compared to methane and thus silane has the higher boiling point. Methane and silane are both nonpolar with only London Forces for intermolecular interactions. ...
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