For a reaction $A+B \longrightarrow$ Products, the rate law is - Rate $=k[A][B]^{3 / 2}$. Can the reaction be an elementary reaction? Explain.
During an elementary reaction, the number or atoms or ions colliding to react is referred to as molecularity. Had this been an elementary reaction, the order of reaction with respect to $B$ would have been 1, but in the given rate law it is $\frac{3}{2}$. This indicates that the reaction is not an elementary reaction. Hence, this reaction must be a complex reaction.
For a certain reaction large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?
According to collision theory apart from the energy considerations, the colliding molecules should also have proper orientation for effective collision.
This condition might not be getting fulfilled in the reaction as it shows the number of reactants taking part in a reaction, which can never be zero.
For a zero order reaction will the molecularity be equal to zero? Explain.
No, the molecularity can never be zero or a fractional number as it shows the number of reactants taking part in a reaction which can never be zero.
For a general reaction $A \rightarrow B$, plot of concentration of $A$ vs time is given in figure. Answer the following questions on the basis of this graph.
(i) What is the order of the reaction?
(ii) What is the slope of the curve?
(iii) What are the units of rate constant?
(i) For $A \longrightarrow B$ the given graph shows a zero order reaction. Mathematically represented as
$$[R]=-k t+[R]_0$$
Which is equation of straight line. Hence, reaction is a zero order.
(ii) Slope $=-k$
(iii) Unit of zero order reaction is $\mathrm{mole~L}^{-1} \mathrm{~s}^{-1}$.
The reaction between $\mathrm{H}_2(g)$ and $\mathrm{O}_2(g)$ is highly feasible yet allowing the gases to stand at room temperature in the same vessel does not lead to the formation of water. Explain.
Because activation energy of the reaction is very high at room temperature but at high temperature H - Hand O - O bond break and colliding particles cross the energy barrier. This is why reaction between $\mathrm{H}_2(\mathrm{~g})$ and $\mathrm{O}_2(\mathrm{~g})$ does not lead to formation of water at room temperature while keeping in the same vessel.