consider the general gas-reaction of a molecular substance, A 1. A-> B At very l

Question

consider the general gas-reaction of a molecular substance, A 1. A-> B At very low pressure how many such reactions occur by the following mechanism 2. A+A -> A* + A (slow) 3. A*+B (fast)
A. Which of the three reactions above is/are elementary?
B. Where appropriate, identity The molecularity of the reaction?
C. What is/are the intermediates and catalysts?
D. Given the mechanism above, suggest a like the rate law for the reaction. 8. Consider the general gas-phase reaction of a molecular substance, A (8 Points) 1.AB At very low pressures many such reactions occur by the following mechanism 2, A + A A* +A (slow) 3, A*-B (fast)

Explanation / Answer

(a) Reaction 2 and 3 are elementary because these complete in one step but reaction 1 is not elementary because it follows a mechanism.

(b) for reaction 1 we can not define molecularity because it follows a mechanism while for elementary reaction, reaction 2 there are 2 molecule are taking part in so molecularity is two and for reaction 3 only one molecule is taking part in reaction so it's molecularity is one.

(c) intermediate is A* , because it is not the part of main reaction (i.e. reaction 1)

(d) rate law is defined using the slow step of a mechanism so from above mechanism reaction 2 is slow so rate law

R = K [A] [A]

this rate law doesn't involve any intermediate, only reactants are involved so it will be the final rate law of mechanism (Note : if rate law incolves any intermediate than we have to eleminate that intermediate)

so final rate law R = K [A]2 where k is rate constant and order of reaction is 2

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