# If the reaction is first order in #A# and second order in #B#, what is the rate constant if #[A] = "0.40 M"# and #[B] = "0.14 M"#?

##### 1 Answer

Well, I can't figure out what all your numbers are, but I can give you a general idea of what to do.

You know that the reaction is first order in

#r(t) = k[A][B]^2#

You know that

There's nothing much you need to do here but plug things in and solve using some simple algebra.

#color(blue)(k = (r(t))/([A][B]^2))#

Since

#"M/s" = ("k units")*"M"^3#

#"k units" = 1"/""M"^2*"s"#