If the concentration units are reduced by n times, then what will be the affect on rate constant if it is a first order reaction?

It will not change

If the concentration units are reduced by a factor of n times, the rate constant (k) for a first-order reaction will remain unchanged.

In a first-order reaction, the rate law equation is given by:

Rate = k[A]

Here, [A] represents the concentration of the reactant, and k is the rate constant. The rate constant is specific to the reaction and remains constant under different concentration units.

When the concentration units are reduced by a factor of n, the new concentration ([A]') can be related to the original concentration ([A]) by the equation:

[A]' = [A]/n

Substituting this into the rate law equation, we have:

Rate = k[A]' = k([A]/n) = (k/n)[A]

Comparing this with the original rate equation, we can see that the rate constant remains unchanged as it appears as a separate term. Therefore, the effect on the rate constant for a first-order reaction is that it will not change if the concentration units are reduced by a factor of n.