Lec-09-Chap13-1-bare

# Lec-09-Chap13-1-bare - Lec-09-Chap13-1-bare Lec-09...

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Lec-09-Chap13-1-bare 9/21/2011 Directionality of Chemical Reactions Entropy Changes. 3 rd Principle. Standard Molar Entropies. 2 nd Principle 1 Lec-09: Thermodynamics: Spontaneous Processes. Entropy and Free Energy Chapter 13 1 Room Assignments Solar ID Room 000000000 – 107757371 Javits 100 Main Floor 107757372 – 999999999 Javits 100 Balcony Dependence of the rate constant with temperature The Arrhenius Equation More energy is available to the reaction system as the temperature increases. E a is the activation energy (units of energy, kJ mol –1 ) R is the gas constant (kJ K –1 mol –1 ) T is the temperature (K) 2   frequency factor (same u rate nits constant as ) a k E RT A e kT This leads to a temperature dependence of the rate constant . Experimentally Arrhenius found:

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Lec-09-Chap13-1-bare 9/21/2011 Directionality of Chemical Reactions Entropy Changes. 3 rd Principle. Standard Molar Entropies. 2 nd Principle 2 Dependence of the rate constant with the temperature Potential Energy Reaction Progress R P E R E P E af E ab Δ E af ab E EE  forward reaction reac pro t ds ants uct Activation energy for the forward reaction reverse reaction r pr ea oducts ctants Activation energy for the reverse reaction 3 4 2 2 3 2 HCl H C CH H C CH Cl 2 2 3 2 3 2 3 2 Step 1: HCl H C CH H C CH + Cl Step 2: H C CH Cl  1 a E 1 a E 2 a E E Which step is rate limiting, 1 or 2? Order of the reaction, 1 or 2 or 3? Endothermic (A) or Exothermic (B)? ANS: 1 ANS: 2 ANS: B
Lec-09-Chap13-1-bare 9/21/2011 Directionality of Chemical Reactions Entropy Changes. 3 rd Principle. Standard Molar Entropies. 2 nd Principle 3 Elementary Reactions       rate constant A r te B a mn tt t k The rate law , frequently of the form reflects instead the detailed series of elementary reaction steps by which the chemical reaction proceeds . 5 A valid reaction mechanism should: Consist of a series of unimolecular and bimolecular elementary reactions. Consist of reaction steps that sum to the overall reaction equation. Correctly predict the experimental rate law. There are two only two important types of elementary reactions: Elementary Reactions - continued a different Unimolecula partic the structure of rearranges to produce or . r : a molecu le or particl ion A le B es (atoms, molecules, or ions) react with each other and yiel prod ucts A Bimolecular: BC two p articles AB d C CD   rate A k    rate k 6

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Lec-09-Chap13-1-bare 9/21/2011 Directionality of Chemical Reactions Entropy Changes. 3 rd Principle. Standard Molar Entropies. 2 nd Principle 4 Mechanism with a Slow Initial Step       22 2 2NO g F g 2NO F g  7     1 2 2 2 2 slo NO F N NO w fa F F F + t O + s F k k  The slowest elementary process in a sequence is called the rate determining step .
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Lec-09-Chap13-1-bare - Lec-09-Chap13-1-bare Lec-09...

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