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NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

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Question : 1 of 39
Marks: +1, -0
From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.
(i) 3NO(g)→N2O(g);3 \mathrm{NO}_{(g)} \rightarrow \mathrm{N}_{2} \mathrm{O}_{(g)} ; Rate =k[NO]2=k[\mathrm{NO}]^{2}
(ii) H2O2(aq)+3I(aq)−+2H+→\mathrm{H}_{2} \mathrm{O}_{2(aq)} + 3 \mathrm{I}^{-}_{(aq)} + 2 \mathrm{H}^{+} \rightarrow 2H2O(l)+I3−;2 \mathrm{H}_{2} \mathrm{O}_{(l)} + \mathrm{I}_{3}^{-} ; Rate =k[H2O2][I−]=k[\mathrm{H}_{2} \mathrm{O}_{2}][\mathrm{I}^{-}]
(iii) CH3CHO(g)→CH4(g)+CO(g);\mathrm{CH}_{3} \mathrm{CHO}_{(g)} \rightarrow \mathrm{CH}_{4(g)} + \mathrm{CO}_{(g)} ; Rate =k[CH3CHO]32=k[\mathrm{CH}_{3} \mathrm{CHO}]^{\frac{3}{2}}
(iv) C2H5CI(g)→C2H4(g)+HCl(g);\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CI}_{(g)} \rightarrow \mathrm{C}_{2} \mathrm{H}_{4(g)} + \mathrm{HCl}_{(g)} ; Rate =k[C2H5Cl]=k[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}]
Solution:  
(i) Order =2,=2, Dimensions of k=Rate[NO]2k = \frac{\text{Rate}}{[\mathrm{NO}]^{2}}
=mol L−1 s−1(mol L−1)2=L mol−1 s−1= \frac{\mathrm{mol}\,\mathrm{L}^{-1}\,\mathrm{s}^{-1}}{(\mathrm{mol}\,\mathrm{L}^{-1})^{2}} = \mathrm{L}\,\mathrm{mol}^{-1}\,\mathrm{s}^{-1}
(ii) Order =2,=2, Dimensions of k=L mol−1 s−1k = \mathrm{L}\,\mathrm{mol}^{-1}\,\mathrm{s}^{-1}
(iii) Order =32,= \frac{3}{2},
Dimensions of k=Rate[CH3CHO]3/2= \frac{\text{Rate}}{[\mathrm{CH}_{3} \mathrm{CHO}]^{3/2}}
=mol L−1 s−1(mol L−1)3/2=L1/2 mol−1/2 s−1= \frac{\mathrm{mol}\,\mathrm{L}^{-1}\,\mathrm{s}^{-1}}{(\mathrm{mol}\,\mathrm{L}^{-1})^{3/2}} = \mathrm{L}^{1/2}\,\mathrm{mol}^{-1/2}\,\mathrm{s}^{-1}
(iv) Order =1,=1, Dimensions of k=Rate[C2H5Cl]k = \frac{\text{Rate}}{[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}]}
=mol L−1 s−1mol L−1=s−1= \frac{\mathrm{mol}\,\mathrm{L}^{-1}\,\mathrm{s}^{-1}}{\mathrm{mol}\,\mathrm{L}^{-1}} = \mathrm{s}^{-1}
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