What is rate constant?

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Jasmine Grover

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Rate Constant:

The rate constant (k) is a proportionality constant that relates the rate of a chemical reaction to the concentrations of the reactants.

  • It is defined as the rate of reaction when the concentrations of all reactants are 1 M.
  • The rate constant depends on the nature of the reaction, the temperature, and the presence of catalysts.

Units of Rate Constant:

The units of the rate constant depend on the order of the reaction.

  • For a first-order reaction, the units of k are s-1 (or reciprocal seconds).
  • For a second-order reaction, the units of k are M-1s-1 (or inverse molarity seconds).
  • For a third-order reaction, the units of k are M-2s-1 (or inverse molarity squared seconds).

The units of k for higher-order reactions can be obtained by generalizing this pattern.

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CBSE CLASS XII Related Questions

  • 1.

    Explain the Finkelstein reaction.


      • 2.

        Conductivity of \( 2.5 \times 10^{-4} \) M methanoic acid solution is \( 5.25 \times 10^{-5} \) S cm\(^{-1}\).

        (a) Calculate its molar conductivity.

        (b) Calculate its degree of dissociation.

        [Given : \( \lambda^{\circ}_{(\mathrm{H^+})} = 349.5 \) S cm\(^2\) mol\(^{-1}\) and \( \lambda^{\circ}_{(\mathrm{HCOO^-})} = 50.5 \) S cm\(^2\) mol\(^{-1}\)]


          • 3.

            (i) Why do Zr and Hf exhibit similar properties ?

            (ii) "\( E^\circ \) for \( \mathrm{Mn^{3+}/Mn^{2+}} \) couple is more positive than that for \( \mathrm{Fe^{3+}/Fe^{2+}} \)." Justify the statement.

            [Atomic number : Mn = 25, Fe = 26]


              • 4.

                A reaction \( \mathrm{A \rightarrow B} \) follows second order kinetics. How will the rate of reaction be affected if the concentration of (i) A is increased by three times, and (ii) A is reduced to half ?


                  • 5.
                    Write the name of basic building units of proteins and nucleic acids. How can you differentiate between Fibrous and Globular proteins on the basis of their structures ?


                      • 6.
                        Consider the decomposition of hydrogen peroxide \( (\mathrm{H_2O_2}) \) as per the equation given below : \[ 2\mathrm{H_2O_2} \xrightarrow[\text{Alkaline medium}]{I^-} 2\mathrm{H_2O} + \mathrm{O_2} \] The mechanism for this reaction was found to be : Step I : \( \mathrm{H_2O_2} + I^- \longrightarrow \mathrm{H_2O} + IO^- \) (slow) Step II : \( \mathrm{H_2O_2} + IO^- \longrightarrow \mathrm{H_2O} + I^- + \mathrm{O_2} \) (fast) (a) Write the rate law expression. (b) Determine the order of reaction with respect to \( \mathrm{H_2O_2} \), \( I^- \) and overall order of reaction. (c) What is the molecularity of the reaction in Step II ?

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