14 - Spontaneous Processes and Equilibrium

14 - Spontaneous Processes and Equilibrium - 8 pm Review...

Info iconThis preview shows pages 1–15. Sign up to view the full content.

View Full Document Right Arrow Icon
38 Review tonight (in here!) 8 pm 7 p.m.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
39 Gibbs Free Energy Three state functions: E, H, S H (enthalpy) and S (entropy) are most important A fourth state function, G, connects both H and S together G = H ± TS G is the Gibbs Free Energy
Background image of page 2
40 Gibbs Free Energy G is the Gibbs Free Energy ' G sys > 0 ' G sys = 0 ' G sys < 0 Non-spontaneous process Reversible process Spontaneous process ' G = ' H -T ' S For chemical reactions at a constant temperature
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
41 Gibbs Free Energy This is just like the enthalpy ( ' H o ) discussion we had last time.
Background image of page 4
42 Gibbs Free Energy ' G = ' H -T ' S Entropy determines the temperature-dependence of ' G Gases exhibit the largest T dependence Followed by solutions Followed by solids Why is this? Think about the statistical definition of entropy.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
43 Gibbs Free Energy & Chemical Equilibrium >@ > @ ln cd ab aA bB cC dD GR T K CD K AB ± ± ²' This is the equation that we want to get to
Background image of page 6
44 Gibbs Free Energy & Chemical Equilibrium Characteristics of Equilibrium States They display no macroscopic evidence of change They are reached through spontaneous processes They show a dynamic balance of forward and reverse processes They are the same regardless of direction of approach
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
45 Empirical Law of Mass Action aA + bB Ù cC + dD Consider the following general reaction Regardless of the initial conditions, once this system has reached equilibrium, the value of the ratio: > @ > @ >@>@ b eq a eq d eq c eq B A D C K Remains constant! This is the law of mass action
Background image of page 8
46 Reaction Coordinates Before we apply the concepts of the law of mass action, let±s cover some of the basic issues related to how chemical reactions proceed We start with reaction coordinate diagrams
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
47 Reaction Coordinate Diagrams E Reaction Coordinate reactants products E a ' E E a = energy of activation (not a state function) ' E = energy difference (usually ' G) between reactants and products (a state function) H + I 2 HI + I H---I---I transition state
Background image of page 10
48 E Reaction Coordinate (distance) reactants products E a ' E H + I 2 HI + I H---I---I transition state question: If I knew ' E, then I could, using what I have learned to date in Chem 1B, calculate the amount of products and reactants at equilibrium. True False
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
49 Equilibrium and ' G o E Reaction Coordinate reactants products ' G ± 1 ' G o A+B C+D transition state > @ > @ >@>@ b eq a eq d eq c eq P B A D C K Assume aA + bB Ù cC + dD in the gas phase, then ' G ± -1 ' G o = Gibbs free energy difference between reactants & products ' G ± 1 = energy barrier separating reactants & products in the forward direction – sort of like E a ' G ± -1 = energy barrier separating reactants & products in the reverse direction True or False ' G o 1 = ' G o -1
Background image of page 12