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Order of Reaction - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

Quick Facts

  • Important Points About Order of Reaction is considered one the most difficult concept.

  • 40 Questions around this concept.

Solve by difficulty

For the reaction A+2B\rightarrow C, rate is given by R=\left [ A \right ]\left [ B \right ]^{2}  then the order of the reaction is

Consider the reaction :

The rate of reaction for this reaction is

Rate =K\left [ Cl_{2} \right ]\left [ H_{2}S \right ]

Which of these mechanism is/are consistent with this rate equation ?

A\: \: \: \: Cl_{2}+H_{2}S\rightarrow H^{+}+Cl^{-}+Cl^{+}+HS^{-}\left ( slow \right )

        \: \: \: \: Cl^{+}+HS^{-}\rightarrow H^{+}+Cl^{-}+S\left ( fast \right )

B\: \: \: \: H_{2}S\Leftrightarrow H^{+}+HS^{-}\left ( fast\: equilibrium \right )

        Cl_{2}+HS^{-}\rightarrow 2Cl^{-}+H^{+}+S\left ( Slow \right )



What is the order of a chemical reaction if the rate depends on the concentration of single reactant raised to the power of 1 / 2?

During the course of a first order chemical reaction, the rate of a reaction

Which among the following will be the unit of rate constant for a homogeneous elementary reaction, A + B → C

For a chemical reaction A + B \rightarrowProduct, the order is 1 with respect to A and B. 

\begin{array}{|c|c|c|} \hline \begin{array}{c} \text { Rate } \\ \mathrm{molL}^{-1} \mathrm{~S}^{-1} \end{array} & \begin{array}{c} {[\mathrm{A}]} \\ \mathrm{molL}^{-1} \end{array} & \begin{array}{c} {[\mathrm{B}]} \\ \mathrm{molL}^{-1} \end{array} \\ \hline 0.10 & 20 & 0.5 \\ \hline 0.40 & \mathrm{x} & 0.5 \\ \hline 0.80 & 40 & \mathrm{Y} \\ \hline \end{array}

What is the value of x and y?

Consider an elementary reaction \mathrm{3 A \rightarrow 2 B+C}. If the concentration of \mathrm{'A'} is tripled, how will the rate of the reaction change?

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Identify the correct statement for a chemical reaction 2A → 3B, 


 If the time for half reaction gets doubled on doubling the initial concentration of the reactants, which among the following is the order of the reaction - 


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At particular concentration, the half life of the reaction is 200 minutes. When the concentration of the reactant become double half life becomes, 50 minutes, then what among the following will be the order of the reaction?


Concepts Covered - 3

Important Points About Order of Reaction

Order of reaction is defined as the number of reactants which determine the rate of reaction. In other words, it is the sum of exponents raised on active masses of reactants in a rate law equation.
Let us consider this reaction
Rate law equation for the reaction can be given as:

               \begin{array}{l}{\mathrm{R} \propto[\mathrm{A}]^{p}[\mathrm{B}]^{q}} \\\\ {\mathrm{R}=\mathrm{K}[\mathrm{A}]^{\mathrm{p}}[\mathrm{B}]^{\mathrm{q}}}\end{array}
\text { Order of reaction }=\mathrm{p}+\mathrm{q}
Rate constant and order for various reacting species is an experimental finding and cannot be predicted directly from the stoichiometry of the balanced reaction.

  1. It is an experimental value.

  2. It may be zero, negative or in fraction.

  3. Order of reaction depends upon temperature, pressure and concentration etc.

  4. It determines rate of reaction.

  5. Order of reaction is determined by the slowest step of the reaction.

  6. High order reactions are rare due to less chance of effective collisions between molecules.

  7. Anything in excess is not counted in order of the reaction. Example, in hydrolysis of ester and sugar water is in excess so it is neglected for order.

Simple/Elementary Single Step Reaction
  • In a complex reactions, there are many steps. Among those only one step is the rate-determining step as it is a slow reaction.
  • The order of the reaction can be found out using the stoichiometric coefficients of the rate-determining step or the slowest step.
  • In a simple reaction, the reaction completes in one single step and that is the rate-determining step. For simple reactions, Gulberg and Waage law of mass action is valid.
    For example:
    \mathrm{H_{2}\: +\: I_{2}\rightarrow 2HI}
    Since it is a simple reaction, thus the rate of reaction is given as:
    \mathrm{Rate\: =\: K[H_{2}]^{1}[I_{2}]^{1}}
Initial Rate Method to Determine Correct Rate Law and Order of Reaction

Consider the reaction:

\mathrm{2A\: +\: B\: \rightarrow P}

The rate law for this reaction is given as follows:

\mathrm{Rate\: =\: K[a]^{x}[B]^{y}}

Now, x and y are the coefficients that are determined experimentally.

K = Rate constant
x,y = Order of reaction with respect to A and B.

Study it with Videos

Important Points About Order of Reaction
Simple/Elementary Single Step Reaction
Initial Rate Method to Determine Correct Rate Law and Order of Reaction

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