Question

For the reaction, ${{\text{H}}_{\text{2}}}\text{(g)+B}{{\text{r}}_{\text{2}}}\text{(g)=2HBr(g),}$ the reaction rate= $K[{{H}_{2}}]{{[B{{r}_{2}}]}^{1/2}}$ which statement is true about this reaction?
A. The reaction is second order
B. Molecularity of the reaction is 3/2
C. The unit of K is $\text{se}{{\text{c}}^{\text{-1}}}$
D. Molecularity of the reaction is 2

Answer 1

Hint: In chemistry we use molecularity generally to define the number of molecules or ions that participate in the rate determining step.
The rate of reaction is defined as the speed at which a chemical reaction takes place(means speed at which reactants get converted into products).
K represent the unit of rate constant, and its formula is \[{{\text{M}}^{\text{1-n}}}{{\text{t}}^{\text{-1}}}\]
Rate of reaction is calculated by K times the concentration of the reacting species.
So lets us see the complete solution by the help of these hints.

Complete step by step solution:

The molecularity is defined as the number of molecules or ions that participate in the chemical reaction.
${{\text{H}}_{\text{2}}}\text{(g)+B}{{\text{r}}_{\text{2}}}\text{(g)=2HBr(g),}$ here we can see that one molecule of hydrogen and one molecule of bromine participate in the reaction, therefore the molecularity of the reaction is 2.
The order of the reaction $K[{{H}_{2}}]{{[B{{r}_{2}}]}^{1/2}}$can be calculated by adding the adding of the power of $\text{B}{{\text{r}}_{\text{2}}}\text{ and }{{\text{H}}_{\text{2}}}$ which gives us 3/2.
So, from above we can conclude that the molecularity if the reaction is 2. Therefore, the correct option is D.

Note: Some shortcuts to find the rate of the reaction-
If you increase the order of the reaction but the rate does not change then it is a zero order reaction.
If you multiply your reactant concentration with the same number you multiply your rate then it is a first order reaction.