Explanation:
Rate of the given reaction is doubled when concentration of ' A ' is doubled and it is quadrupled when concentrations of ' A ' and ' B ' are raised four times.
Let the rate, \({\rm{R = k}}{[{\rm{A}}]^{\rm{x}}}{[{\rm{B}}]^{\rm{y}}}\,\,\,\,(1)\)
\({\mathrm{\therefore}}\) When concentration of \({\mathrm{A}}\) is doubled, the new rate \({\mathrm{\left(R_{1}\right)}}\) will be
\({{\rm{R}}_{\rm{1}}}{\rm{ = k}}{[{\rm{2A}}]^{\rm{x}}}{[{\rm{B}}]^{\rm{y}}}\,\,\,\,\,\,\,\,\,\,\,\,\,(2)\)
But \({\mathrm{\mathrm{R}_{1}=2 \mathrm{R}}}\)
\(\therefore \,\,\,{\rm{k}}{[{\rm{2A}}]^{\rm{x}}}{[{\rm{B}}]^{\rm{y}}}{\rm{ = 2k}}{[{\rm{A}}]^{\rm{x}}}{[{\rm{B}}]^{\rm{y}}}\)
\(\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\mkern 1mu} [{\rm{From(1)}}{\mkern 1mu} {\rm{and }}({\rm{2}})]\)
\({\mathrm{\therefore k 2^{\mathrm{x}}[A]^{\mathrm{x}}[B]^{\mathrm{y}}=2 \mathrm{k}[\mathrm{A}]^{\mathrm{x}}[B]^{\mathrm{y}}}}\)
\({\mathrm{\therefore \quad 2^{x}=2}}\) and thus \({\mathrm{x=1}}\)
Similarly, when concentrations of both \({\mathrm{A}}\) and \({\mathrm{B}}\) are quadrupled, the new rate \({\mathrm{\left(\mathrm{R}_{2}\right)}}\) will be\({{\rm{R}}_{\rm{2}}}{\rm{ = k}}{[{\rm{4}}\;{\rm{A}}]^{\rm{x}}}{[{\rm{4}}\;{\rm{B}}]^{\rm{y}}}\,\,\,\,\,\,\,\,\,\,\,\,(3)\)
But \({\mathrm{\mathrm{R}_{2}=4 \mathrm{R}}}\)
\(\therefore \,\,{\rm{k}}{[{\rm{4}}\;{\rm{A}}]^{\rm{x}}}{[{\rm{4}}\;{\rm{B}}]^{\rm{y}}}{\rm{ = 4k}}{[{\rm{A}}]^{\rm{x}}}{[{\rm{B}}]^{\rm{y}}}\quad \)
\(\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,[From(1)\,and\,(3)]\)
\({\mathrm{K 4^{x}[A]^{x} 4^{y}[B]^{y}=4 k[A]^{x}[B]^{y}}}\)
\({\mathrm{\therefore 4^{x} \cdot 4^{y}=4}}\)
\({\mathrm{\therefore \quad 4.4^{\mathrm{y}}=4 \quad(\because \mathrm{x}=1)}}\)
\({\mathrm{\therefore \quad 4^{y}=1}}\) and thus \({\mathrm{y=0}}\)
Substituting the values of \({\mathrm{x}}\) and \({\mathrm{y}}\) in (1), the rate expression for the given reaction is
rate, \({\mathrm{\mathrm{R}=\mathrm{k}[\mathrm{A}]^{1}[\mathrm{~B}]^{0} \quad \therefore \quad \mathrm{R}=\mathrm{k}[\mathrm{A}]}}\)
Thus, the overall order of the given reaction is 1 .