(50 pts) You study this reaction and experimentally find it to be first order in

Question

(50 pts) You study this reaction and experimentally find it to be first order in both hydrogen bromide and oxygen and propose the following mechanism: H Br (g) + O2 (g) HOOBr (g) HOOBr (g) + HBr (g) 2 HOBr (g) HOBr (g) + HBr (g) H2O (g) + Br2(g) HOBr (g) + HBr (g) H2O(g) + Br2(g) (a) Write the balanced equation for this reaction of hydrogen bromide gas with oxygen to produce water vapor and bromine gas: (b) Show how this mechanism complies with one of the three requirements for mechanisms to be considered valid: (c) If the experimental rate law is found to be: rate k [HBr] IO], which of the above three steps is rate determining? Why? (d) List any intermediates present in this mechanism.

Explanation / Answer

Part a

To get the balanced equation

Add all the equations

HBr + O2 + HOOBr + 2HOBr + 3HBr = HOOBr + 2HOBr + 2H2O + 2Br2

4HBr + O2 = 2H2O + 2Br2

Part b

Three requirements for valid mechanism

1-on adding the elementary steps, it gives the overall balanced equation.

2. The elementary steps should be unimolecular bimolecular. 3. the rate law must correlate with the mechanism.

The first requirement is satisfied from part a, therefore the mechanism is to be considered valid

Part C

Rate law = k [HBr] [O2]

The mechanism is valid so rate law must correlate with the mechanism.

Rate law for the first elementary step

Rate law = k [HBr] [O2]

Since the rate law is same. The first elementary step is rate determining.

Part d

Intermediates are not in the product list

HOOBr & HOBr are intermediates

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