Ch1b09Lecture15

Ch1b09Lecture15 - A few words on Go So Ho Catalysts Acids...

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1 •A few words on Δ G o , Δ S o , Δ H o •Catalysts •2 chemistry in context examples +
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2 Chemical catalysts accelerate reactions but don’t change equilibria
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15 Acids and Bases: an extension of chemical equilibria J. N. Bronsted, 1879 - 1947 T. M. Lowry, 1874 - 1936 G. N. Lewis 1875 - 1946 You should think in terms of electron donors and acceptors! Protons!! Think proton donors and acceptors. I think Bronsted is on to something. ..
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16 Bronsted-Lowry Model for Acids and Bases An acid is a proton (H + ) donor A base is a proton (H + ) acceptor In an acid-base reaction, one or more protons are transferred from the acid molecule to the base molecule: HA(aq) + B ¯ (aq) A ¯ (aq) + HB(aq) In the above reaction HA is the acid and B ¯ is the base.
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17 The species produced when a proton leaves an acid is known as the conjugate base of that acid. In a similar fashion, the species that is formed when the base adds a proton is the conjugate acid of that base: Conjugate Acids and Bases HA(aq) + B ¯ (aq) A ¯ (aq) + HB(aq) A ¯ is the conjugate base of the acid HA HB is the conjugate acid of the base B ¯
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18 Lewis Model for Acids and Bases This definition is more general than the Bronsted-Lowry definition. Obviously, H + is an acid and OH ¯ is a base under either definition, since for a proton to bind to a base, it must accept a pair of electrons: H + (aq) + :OH ¯ (aq) H 2 O(l) • An acid is an electron pair acceptor • A base is an electron pair donor
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19 ¯ + BF 3 + NH 3 F 3 B-NH 3 (dative bond) The Lewis definition extends beyond just the proton. For example, consider the reaction of BF 3 (a Lewis acid) with NH 3 (a Lewis Base): Lewis Model for Acids and Bases Cu +2 (aq) + 4NH 3 (aq) Cu(NH 3 ) 4 +2 (aq) Cu +2 accepts four pairs of electrons from the ammonia molecules, so it is an acid. The ammonia molecules are donating their lone pairs, so the ammonia molecules are the bases.
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20 Water Autoionization Water can act both as an acid and a base, and can do so even without the presence of another species. The reaction between two water molecules is 2H 2 O(l) Ù H 3 O + (aq) + OH ¯ (aq) or, more simply, H 2 O(l) Ù H + (aq) + OH ¯ (aq) The equilibrium constant expression for this reaction is: K w = [H + ][OH ¯ ] Pure liquids and solids do not enter into the expression. For water at 25 0 C, K w is 1.0 x 10 -14 .
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21 Strong Acids and Bases Strong acids are completely ionized in aqueous solution: HCl, HBr, HI, H
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This note was uploaded on 09/25/2010 for the course CH 104 taught by Professor Bopanna during the Fall '09 term at UMBC.

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Ch1b09Lecture15 - A few words on Go So Ho Catalysts Acids...

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