CHP%202%20Water - Chapter 2 Water Weak Interactions in...

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1 Chapter 2 Water Chapter 2 2 Water is the Solvent for Living Cells Weak Interactions in Aqueous Systems • The attractions between adjacent water molecules gives liquid water great internal cohesion and leads to its unusual properties. • The electrostatic interaction between the hydrogen atom of one water molecule and the oxygen atom of another yields the hydrogen bond. • This bonds are relatively weak with bond dissociation energies of about 23 kJ/mol compared to 470 kJ/mol for the covalent hydroxy bond.
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2 Chapter 2 3 Weak Interactions in Aqueous Systems The tetrahedral arrangement of the water molecule gives each molecule the potential to form 4 hydrogen bonds (1 for each hydrogen and 2 for the oxygen) In the liquid state, the disorganization of the molecules yields an average of 3.4 bonds per molecule In the solid state, the fixed nature of the molecule in the crystal lattice yields the full hydrogen bonding compliment. The number of hydrogen bonds possible in both states results in the high melting and boiling points for water This hydrogen bonding pattern gives water unique properties: – High boiling and melting points – High surface tension – A lower density in the solid state compared to the liquid state Chapter 2 4 Though a small molecule, water is powerful… Weak Interactions in Aqueous Systems
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3 Chapter 2 5 Colligative Properties of Water Weak Interactions in Aqueous Systems Colligative Properties depend ONLY on the number of solute particles in solution, NOT on the identity of the solute. Vapor pressure lowering Freezing point depression Boiling point elevation Osmotic pressure • These particles affect properties of the solvent by lowering the effective concentration of the solvent • For water, the presence of a solute disrupts the hydrogen bonding network Chapter 2 6 Energetics of Solution Formation ( S soln ) Weak Interactions in Aqueous Systems G = H – T S
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4 Chapter 2 7 Energetics of Solution Formation ( H soln ) • The solute–solvent interactions are stronger than solute–solute or solvent–solvent. Favorable process • Negative H soln Exothermic H soln Weak Interactions in Aqueous Systems Chapter 2 8 Energetics of Solution Formation ( H soln ) Endothermic H soln • The solute–solvent interactions are weaker than solute–solute or solvent–solvent. Unfavorable process. • Positive H soln Weak Interactions in Aqueous Systems In the end, Like dissolves Like!
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5 Chapter 2 9 “The more complex the system, the weaker are the forces that govern its behavior” - J. R. Platt Weak Interactions in Aqueous Systems the Universe Macromolecules Simple compounds Atoms Atomic nuclei Structure: Most Complex Complex Simple Gravity Non-covalent bonds Covalent bonds Atomic Internuclear Forces: Weakest Weaker Stronger Chapter 2 10 Weak Interactions in Aqueous Systems •A n intermolecular force is an attraction between molecules Intra
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This note was uploaded on 06/03/2008 for the course BIO 150 taught by Professor Kore during the Spring '08 term at Abraham Baldwin Agricultural College.

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CHP%202%20Water - Chapter 2 Water Weak Interactions in...

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