Question

What will be the instantaneous rate of reaction in terms of its reactants for the given equation?
\[2KCl{O_3} \to 2KCl + 3{O_2}\]

Answer 1

Hint: Instantaneous rate of a reaction can be defined as the rate of reaction at any particular time or for a very short period of time. Instantaneous rate of reaction keeps on changing as the concentration of the reactant and product keeps on changing from time to time.

Complete answer: As we know, instantaneous rate of reaction is for a particular instant time.
It is a differential rate of reaction.
So, let’s understand how to calculate it:
We calculate instantaneous rate by calculating the negative of the slope of concentration of the reactant versus time at \[t\] .
So, the formula will be written as:
\[rate = - \dfrac{{\Delta \left( {{\text{reactant}}} \right)}}{{\Delta t}}\]
\[rate = \dfrac{{\Delta \left( {product} \right)}}{{\Delta t}}\]
So, this is how our differential rate law is written.
One more important point to keep in mind is that while writing the rate law don’t forget to mention the stoichiometric coefficient in the formula.
Example for our given equation:
The instantaneous rate law will be given as:
In terms of reactants: \[rate = - \dfrac{1}{2}\dfrac{{d\left( {KCl{O_3}} \right)}}{{dt}}\]
Keep in mind, here stoichiometric coefficient is also mentioned.

Note:
Here minus sign on the reactant side indicates that the reactant is depleting with the time. We usually don’t put the minus sign while indicating the rate law in terms of the products. And also above in the formula, at one place we have used the symbol delta, \[\Delta \] and at the other the symbol \[d\] . So don’t worry they indicate the same thing i.e. change in amount.