Lecture 2 - Water G= H-T S G free energy change H Entholpy...

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Unformatted text preview: Water G= H-T S G free energy change H Entholpy T Temperature S - Entropy G= H-T S Large increase in Enrtopy, S, is responsible for dissolving of salts (NaCl) in water. Chemical Reactivity When bonds are broken and formed, the difference between energy extracted from surroundings and energy released to the surroundings can be called enthalpy change, H. If energy is absorbed (endothermic), the H is positive. If energy is released (exothermic), the H is negative. Enthalpy- H The change in enthalpy reflects the numbers and kinds of bonds that are made or broken. The H is one of the three factors that determine the free energy change G of the reaction. Enthalpy, H Temperature, T Entropy, S Four Types of Noncovalent Interactions Hydrogen bonds Ionic interactions Hydrophobic interactions Van der Waals interactions Pure Water is Ionized H2O[H+ + [OH-] Hydronium ions H3O+ Ionization of water is expressed by equilibrium constant: Keq Ion product of water Kw=(55.5M) x Keq= [H+ ] x [OH-]=1x10-14M2 The product of [H+ ] x [OH-]= 1x10-14M2 When [H+ ] = [OH-]= 1x10-7M. The pH scale designated the [H+] and [OH-] concentrations pH is negative log of [H+] concentration=> -log[H+]. pH=7 means [H+] concentration of 10-7 and , therefore, [OH-] concentration of 10-7. Weak acids and bases have dissociation constants Acids are proton donors Bases are proton acceptors HA[H+] + [A-] CH3COOH H+ + CH3COO- Ka -dissociation constant pKa of 4.76 means that at pH 4.76 half of the protons have dissociated. ...
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