Question #f17d6

1 Answer
Truong-Son N.
Nov 13, 2017

Well, why not? The units must always work out, don't they?

The units of rate are ALWAYS concentration per unit time. And thus, with fixed rate units and varied reaction order, the rate constant units must change...

Suppose the time unit were seconds and concentration units were #"mol/L"# #-=# #"M"#. For some rate law

#r(t) = k[A]^m[B]^n#,

the units are

#"M"/"s" = [k] cdot "M"^(m)"M"^(n)#,

where #m# and #n# are the orders with respect to each of two reactants.

Then, the units of the rate constant MUST be:

#color(blue)([k] = "M"^(1-m-n)cdot"s"^(-1))#

And thus, the rate constant units clearly depend on the reactant orders.

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