Pyrolysis of acetic aldehyde

The Rice-Herzfeld mechanism for the decomposition of acetaldehyde involves the following steps  

The radical CHO gives other decomposition products that will not be considered here. Applying the steady-state condition we obtain 

The mechanism explains conectly the three-halves order. The overall activation energy is 

To obtain a j order the initiation step can be a first-order process, but the termination step requires the combination of the same two radicals. If in the same mechanism instead of step (4) we have the reaction 

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