Question

3A + B ----> C

what is the limiting reactant ? and what is the unit of k ?

2-

3A + 2B ----> 2C

what is the limiting reactant ? and what is the unit of k ?

Answer 1

Assuming it is a elementary reaction then A is excess reactant and B is limiting reactant.

since we cannot have order greater than 3, we assume that A to be in bulk quantities(as shown in reaction it is more) and that B is only controlling the reaction hence the reaction is of order 1 in B.

so, as order is 1,we have k units as (time)^-1

^{else without assumptions we can only determine k units from experiments}

^{So for second case}

same B will be the limiting reactant and since it controls the reaction and that A is in bulk,assuming A doesnt control reaction,we have 2 order reaction in B.

k units are (concentration)^-1x(time)^-1

else without assumptions we can only determine k units from experiments