The following data refer to the gas-phase substitution reaction: [M(CO) 6 ] (g)
ID: 522394 • Letter: T
Question
The following data refer to the gas-phase substitution reaction: [M(CO)6] (g) + *CO (g) ---> [M(CO)5(*CO)] (g) + CO (g)
2. The following data refer to the gas-phase substitution reaction: (g) CO (g) [M(co) co (g) AS Cr 161.9 77.4 Mo 126.4 -1.7 In AH: cri 166.5 46 169.2 kJ/mol. decalin solution, the 163.2 kJlmoli Mo, 132.2 kJ/mol; w, values a the significance of the agreement between gas phase and solution activation a) hat is enthalpies? Explain. (4 points) Based on the above data and an and d rate dependence on 'co at low concentration, draw a mechanism for the reaction discuss b)Explanation / Answer
What is the significance of the agreement between gasphase and solution activation enthalpies? Explain.
the activation enthalpies are nearly the same.
It suggests that the reaction mechanism in both the gas phase and in decalin must be the same.
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Based on the above data and an observed rate dependence on *CO at low concentration, draw a mechanism for the reaction and discuss it.
The large positive activation entropies clearly imply a dissociative mechanism. Thus, CO dissociation is the first step. Presumably, the five coordinate intermediate generated is then trapped by *CO. The observed rate dependence on *CO at low concentration suggests CO dissociation is reversible
[M(CO)6]---ki/k2-----à M(CO)5 + CO
M(CO)5 --- k2 *CO-----à[M(CO)5 (*CO)] + CO
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What is the form of the reaction rate law at low [*CO]?
rate = -d[M(CO)6]/dt= k1k2[M(CO)6][*CO] / k-1[CO] + k2[*CO]
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What is the form of the reaction rate law at high [*CO]?
At high *CO concentration (or if k2 >> k-1),
the expression above reduces to: rate = k1 [M(CO)6].
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