Composite Reactions & the Steady State Approximation

HALOGENATION OF PROPANONE

Hint

To obtain the steady state concentration:

Step Procedure Example:
0 = + aX - bX + c
1 Move all terms containing the species of interest to the left hand side of the equation. (Remember sign changes.) - aX + bX = + c
2 Rewrite the left hand side of the equation, bringing the species of interest to the front of a bracket (i.e. [Pe]( . . . )). X ( - a + b ) = + c
3 Divide both sides of the equation by the term in the bracket. X ( - a + b ) / ( - a + b ) = + c / ( - a + b )
4 Cancel terms (where appropriate). X = + c / ( - a + b )

Steady State Concentration of the enol form of Propanone {[Pe]ss}

Applying the Steady State Approximation to the overall rate of production of the enol form of proponone, gives

0 = + k1[H+][Pk] - k-1[Pe][H+] - k2[Pe][I2]

On rearrangement, the steady state concentration of the enol form of propanone is found to be

[Pe]ss = + k1[H+][Pk] / (k-1[H+] + k2[I2])

[Pe]ss = - k1[H+][Pk] / (k-1[Pe][H+] - k2[Pe][I2])

[Pe]ss = + k1[H+][Pk] / (k-1[H+] - k2[I2])

[Pe]ss = - k1[H+][Pk] / (k-1[H+] + k2[I2])