Question

What is the units of k in the following expression: rate = k[A][B]?

A) s^-1
B)M^-1 s^-1
C)M^-2 s^-1
D)M

Answer 1

What is the units of k in the following expression: rate = k[A][B]?

A) s^-1
B)M^-1 s^-1
C)M^-2 s^-1
D)M

ans: B

Answer 2

Answer : The correct option is, (B) $M^{-1}s^{-1}$

Explanation:

Rate of reaction : It is defined as the rate of change in concentration of reactant or product with respect to time.

The given rate expression is,

$Rate=k[A][B]$

From this expression we conclude that the power of concentration of reactant A and B are 1, 1. That means it is a second order reaction.

The formula for determining the unit of 'k' is:

$\text{Unit}=\frac{(Concentration)^{1-n}}{Time}$

where, n = order of reaction

The unit of concentration is, M or mole/L

The unit of time is, second or 's'.

When n = 0

The unit of 'k' = $\frac{(M)^{1-0}}{s}=Ms^{-1}$

When n = 1

The unit of 'k' = $\frac{(M)^{1-1}}{s}=s^{-1}$

When n = 2

The unit of 'k' = $\frac{(M)^{1-2}}{s}=M^{-1}s^{-1}$

and so on.....

Therefore, the unit of 'k' of the following expression is, $M^{-1}s^{-1}$