Question

Define the following terms with a suitable example in each case :
(i) Ambidentate ligand
(ii) Double salt

Hint:

Ambidentate = two possible donor atoms; double salt = dissociates fully in water.

Answer 1

Concept: The overall order of a reaction is just a number. You get it by adding up the powers (the small numbers sitting on top) of the concentration terms in the rate law that comes from experiment.

Step 1: Pick out the powers
Look at the rate law: $\mathrm{Rate = k[A][B]^{3/2}}$. The power on $[A]$ is $1$ (when nothing is written, it means $1$). The power on $[B]$ is $\tfrac{3}{2}$. These are the only two powers we have.

Step 2: Add the powers to get the order
Now simply add them up: \[ \text{order} = 1 + \tfrac{3}{2} = \tfrac{5}{2} = 2.5 \] So the overall order of this reaction is $2.5$.

Step 3: Can it be an elementary reaction?
An elementary reaction is one that happens in a single step, in one clean collision. For such a one-step reaction the order must match the number of molecules taking part, and you cannot have half a molecule colliding. That means the order of an elementary reaction always comes out as a whole number like $1$, $2$ or $3$, never a fraction. Here the order is $2.5$, which is a fraction. A fraction can only show up when the reaction really goes through several steps, in other words a complex reaction. So this one cannot be elementary.

Answer: The overall order is $2.5$. It cannot be an elementary reaction, because the order is a fraction and a single-step reaction can only have a whole-number order.