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Reaction order

A + 2B --> P + Q

third order forward
second order backward

Kd = [P][Q]

When the enzyme is rate limiting, enzymatic reactions are zero order w.r.t. substrate.
First order reactions are rare, but you can make pseudo first-order reactions by having large excesses of the other reactants.
eg. [B] is so large that it doesn't change appreciably over the reaction:
                rate = k[A][B]    becomes    rate = k'[A]
you can tell that it is not true first order because the slope changes with changes in [B]