Chapter 6 Concepts Review
Chapter 6 Concepts Review CHEM 3101
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This 3 page Study Guide was uploaded by Lindsey Rae on Tuesday March 1, 2016. The Study Guide belongs to CHEM 3101 at University of Colorado Colorado Springs taught by John Balyeat in Winter 2016. Since its upload, it has received 39 views.
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Date Created: 03/01/16
Chapter 6 Review 6.1 The total change in enthalpy for any reaction (delta H), also called the heat of reaction, is a measure of the energy exchanged between the system and its surroundings. Each type of bond has a unique bond dissociation energy which is the amount of energy necessary to accomplish hemolytic bond cleavage, producing radicals. Exothermic reactions involve a transfer of energy from the system to the surroundings, while endothermic reactions involve a transfer of energy from the surroundings to the system. 6.2 Entropy is loosely defined as the disorder of a system and is the ultimate criterion for spontaneity. In order for a reaction to be spontaneous the total charge in entropy must be positive. Reactions with a positive Delta S sys involve an increase in he number of molecules, or an increase in the amount of conformational freedom 6.3 In order for a process to be spontaneous, the change in Gibbs free energy must be negative A process with a negative delta G is called exergonic, while a process with a positive delta G is called endergonic 6.4 Equilibrium concentrations of a reaction represent the point of lowest free energy available to the system The exact position of equilibrium is described by the equilibrium constant Keq and is a function of delta G If Delta G is negative, the reaction will favor products over reactants and Keq will be greater than 1. If Delta G is positive, the reaction will favor reactants over products, and Keq will be less than 1 The study of relative energy levels and equilibrium concentrations is called thermodynamics. 6.5 Kinetics is the study of reaction rates. The rate of any reaction is described by a rate equation. A reaction can be first order, second order or third order, depending on whether the sum of the exponents in the rate equation is 1, 2, or 3 respectively. A low energy of activation, Ea, corresponds with a fast rate. Increasing the temp will increase the number of molecules that possess the minimum necessary kinetic energy for a reaction, thereby increasing the rate of reaction. Catalysts speed up the rate of reaction by providing an alternative path way with a lower activation energy. 6.6 Kinetics refers to the rate of a reaction and is dependent of the relative energy levels of the reactants and products. On an energy diagram each peak represents a transition state while each valley represents an intermediate. Transition states cannot be isolated, intermediates will have a finite lifetime. The Hammond postulate states that a transition state will resemble the reactants for an exergonic process but will resemble the products for an endergonic process. 6.7 Ionic reactions also called polar reactions involve the participation of ions as reactants, intermediates or products, in most cases, intermediates. A nucleophile has an electron rich atom that is capable of donating a pair of electrons. Nucleophilic centers include atoms with lone pairs, pi bonds, or atoms that are electron rich due to inductive effects. An Electrophile has an electron deficient atom that is capable of accepting a pair of electrons. Electrophilic centers include atoms that are electron deficient due to inductive effects as well as carbocations which have an empty p orbital. Polarizability describes the ability of an atom to distribute its electron density unevenly as a result of external influences. 6.8 The most common type of rearrangement is a carbocation rearrangement, in which a carbocation undergoes either a hydride shift or a methyl shift to produce a more stable carbocation. As a result of hyper-conjugation, tertiary carbocations are more stable that secondary which are more stable than primary carbocations. 6.9 All ionic mechanisms are different combinations of the four characteristic arrow pushing patterns 6.11 A carbocation rearrangement will occur if it leads to a more stable carbocation Tertiary carbocations typically do not rearrange unless rearrangement will produce a resonance stabilized carbocation such as an allylic carbocation. 6.12 Irreversible reaction arrows are used for a nucleophilic attack involving a strong nucleophile or for a proton transfer in which there is a vast difference in pKa values, or for a carbocation rearrangement. Reversible reaction arrows are used in most other cases.
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