9. 8 The rate theory of unimolecular reaction Extensive reading: Levine, pp. 906-908 Section: 23. 6
9.8 The rate theory of unimolecular reaction Extensive reading: Levine, pp. 906-908 Section: 23.6
9.8 The rate theory of unimolecular reaction ()Theories for bimolecular reactions Transitional energy SCT Threshold energy, Vibrational energy? Potential energy TST ●●●●● Vibrational energy Zero point energy What kind of activation energy do these reactions relate? kalB How can a common molecule get activated? dt
(1) Theories for bimolecular reactions: SCT TST Transitional energy; Threshold energy; Vibrational energy? Potential energy; Vibrational energy; Zero point energy What kind of activation energy do these reactions relate? How can a common molecule get activated? 9.8 The rate theory of unimolecular reaction d[P] [A][B] d k t =
9.8 The rate theory of unimolecular reaction (2) Examples for possible unimolecular reactions decomposition Isomerization (1) Does unimolecular reaction need activation? (2) How does the molecule get activated?
(2) Examples for possible unimolecular reactions decomposition Isomerization + (1) Does unimolecular reaction need activation? (2) How does the molecule get activated? 9.8 The rate theory of unimolecular reaction
9.8 The rate theory of unimolecular reaction 9.8.1 Puzzling problems (1) Does unimolecular reaction need activation? It is obvious that a single molecule at ground state will not undergo any reaction (or this compound is unstable)except that it was activated by energy of some types A—)A P How do reactant molecules acquire necessary activation energy (a) Activation through collision--heat? (b) Activation by energy radiation--work?
It is obvious that a single molecule at ground state will not undergo any reaction (or this compound is unstable) except that it was activated by energy of some types. A ⎯→ A* ⎯→ P How do reactant molecules acquire necessary activation energy？ 9.8.1 Puzzling problems (1) Does unimolecular reaction need activation? (a) Activation through collision—heat? (b) Activation by energy radiation—work? 9.8 The rate theory of unimolecular reaction
9.8 The rate theory of unimolecular reaction 9.8.1 Puzzling problems (a) activation by collision: Before reaction takes place, reactants must collide with each other to acquire enough activation energy. This may lead to a conclusion that all gaseous unimolecular reaction should be second-ordered dP A+M→>A*)P dt IA=k[AJM] At early 19th century, it was found that all unimolecluar reaction, such as gaseous decomposition and isomerization, is of first-order dP klA dt
(a) Activation by collision: Before reaction takes place, reactants must collide with each other to acquire enough activation energy. This may lead to a conclusion that all gaseous unimolecular reaction should be second-ordered. At early 19th century, it was found that all unimolecluar reaction, such as gaseous decomposition and isomerization, is of first-order. A + M ⎯→ A* ⎯→ P dP [A] d k t = 9.8.1 Puzzling problems * 1 dP [A ] [A][M] d k k t = = 9.8 The rate theory of unimolecular reaction