Chapter-6 - Chapter 6: Condensed phases and phase...

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Chapter 6: Condensed phases and phase transitions PV = 22.4 L atm for 1 mol of ideal gas at 0 o C Then 1 mol of a ideal gas will occupy 22.4 L at 1 atm and 273 K. What is the volume of 1 mol of a liquid? Consider H 2 O( l ) as an example. Density of H 2 O( l ) is ~1 g/cc 1 g of H 2 O( l ) occupies 1 cc 18.0148 g of H 2 O( l ) occupies 18.0148 cc 1 mol =18.0148 g of H 2 O( l ) occupies 18.0148 cc =18.0148 mL =0.018 L Thus volume of 1 mol H 2 O( l ) =0.018L Volume of 1 mol gas = 22.4 L at 1 atm and 273 K “Volumes occupied by molecules in condensed phases are ~ 1000 times smaller than the volumes occupied by molecules in gas phase, which is attributed to intermolecular forces . intermolecular forces (a). Are weaker than chemical bonds (b). Less directional than covalent bonds, but more directional than ionic bonds (c). Operate at longer range than covalent bonds,but at shorter range than ionic bonds
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Potential energy curves Energy of attraction and energy of repulsion are a part of potential energy. (a). The deeper the potential energy well, the stronger the interaction between atoms and more energy is required to separate them apart. Internuclear distance Potential energy 0 A-B Two separated atoms Atoms are pushed closer than in chemical bond Repulsive forces dominate Atoms approach each other attractive forces dominate Two atoms form a chemical bond. “ Attractive forces and repulsive forces balance out ”. Energy needs to be supplied to break the bond (b). Interactions such as those in Ar…Ar and HCl…HCl are hundreds of times weaker than those among Cl-Cl and K + ….Cl - . (c). Interactions such as those in Ar…Ar and HCl…HCl are called non-bonded interactions
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Dipole-dipole interactions : when two polar molecules with net dipoles come closer, one end of the dipole in one molecule will be attracted to the opposite end in the second molecule. H Cl + - H + Cl - (a). These forces are strong, but are weaker than ion-ion interactions in ionic compounds. (b). These forces decrease with distance as 1 __ r 3 Ion-dipole interactions : When polar molecules encounter ions, the positive end of the dipole is attracted to negative ions and vice versa. O H H δ + δ + δ - Cl - Na + The ion-dipole interactions require two species to be present, one to provide ions and another to provide dipoles. Induced dipole interactions : In non-polar molecules, electrons are distributed symmetrically. This symmetry can be distorted by an ion/dipole, by inducing dipole in non-polar Na + - + Types of Non-Bonded ( intermolecular, van der Waals) Interactions Dipole-dipole Ion-dipole Induced dipole Dispersion or London Hydrogen bonding ion- ion
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Types of Non-Bonded Interactions ..contd Dispersion or London forces : Noble gases are atomic gases and do not have dipole moments or net charges. The fact that they can be liquefied suggests that forces of attraction exist between atoms of a noble gas. These forces are called Dispersion or London forces.
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This note was uploaded on 04/14/2008 for the course CHEM 116 taught by Professor Prolavarapu during the Fall '06 term at Vanderbilt.

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Chapter-6 - Chapter 6: Condensed phases and phase...

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