H + Free Energy Change C—H AG=free energy of(products-reactants amount of energy available to do work Negative values indicate spontaneity △G=R7(nKe) Wherer=1.987 cal/K-mol and T= temperature in kelvins Since chlorination has a large Kea, the free energy change is large and negative Chapter 4
Chapter 4 11 Free Energy Change • DG = free energy of (products - reactants), amount of energy available to do work. • Negative values indicate spontaneity. • DGo = -RT(lnKeq ) where R = 1.987 cal/K-mol and T = temperature in kelvins • Since chlorination has a large Keq , the free energy change is large and negative. =>
H Problem C——H H Given that X is-oh, the energy difference for the following reaction is.0 kcal/mol What percentage of cyclohexanol molecules will be in the equatorial conformer at equilibrium at25°C? X equatorial X axial Chapter 4
Chapter 4 12 Problem • Given that -X is -OH, the energy difference for the following reaction is -1.0 kcal/mol. • What percentage of cyclohexanol molecules will be in the equatorial conformer at equilibrium at 25°C? =>
Factors determining△G°HH Free energy change depends on >enthalpy >entropy AH=(enthalpy of products)-(enthalpy of reactants) △S°=( entropy of products)-( entropy of reactants) ·△G=△F-7S° Chapter 4
Chapter 4 13 Factors Determining DG • Free energy change depends on Øenthalpy Øentropy • DH = (enthalpy of products) - (enthalpy of reactants) • DS = (entropy of products) - (entropy of reactants) • DG = DH - TDS =>
H + Enthalpy C—H H AHo heat released or absorbed during a chemical reaction at standard conditions EXothermic, (-AR, heat is released Endothermic, (+AR), heat is absorbed Reactions favor products with lowest enthalpy(strongest bonds) Chapter 4
Chapter 4 14 Enthalpy • DHo = heat released or absorbed during a chemical reaction at standard conditions. • Exothermic, (-DH), heat is released. • Endothermic, (+DH), heat is absorbed. • Reactions favor products with lowest enthalpy (strongest bonds). =>
H + Entropy C—H H ASo change in randomness, disorder freedom of movement Increasing heat, volume, or number of particles increases entropy Spontaneous reactions maximize disorder and minimize enthalpy In the equation AGo= AHo TAso the entropy value is often small Chapter 4 15
Chapter 4 15 Entropy • DSo = change in randomness, disorder, freedom of movement. • Increasing heat, volume, or number of particles increases entropy. • Spontaneous reactions maximize disorder and minimize enthalpy. • In the equation DGo = DHo - TDSo the entropy value is often small. =>