Units of rate constant
For a general reaction
aA + bB ® cC + dD
Rate = k [A]
x  [B]
y
Where x + y = n = order of the reaction
k = 
x
Rate
[A] [B]y
(
)
(
)
=
n
concentration
1
=
×
where [A] [B]
time
concentration
Taking SI units of concentration, mol L
–1 and time, s, the units of
k for different reaction order are listed in Table 3 3
Table 3 3: Units of rate constant
Reaction
Order
Units of rate constant
Zero order reaction
0
(
)
1
1
1
10
mol L
1
mol L s
s
mol L
−
−
−
−
×
=
First order reaction
1
(
)
1
1
11
mol L
1
s
s
mol L
−
−
−
×
=
Second order reaction
2
(
)
1
1
1
12
mol L
1
mol L s
s
mol L
−
−
−
−
×
=
Identify the reaction order from each of the following rate constants (i) k = 2