The activation energy for a reaction is 84.0kJ/mol. Addition of a catalyst lowers the activation energy by 23.0 kJ/mol, while leaving the A-factor unchanged. By what factor ( uncatalyzed catalyzed k k ) does the rate increase at 25 °C?

Answer :

Answer : The rate constant of the reaction is increased by factor, [tex]4.93\times 10^{10}[/tex]

Solution :

According to the Arrhenius equation,

[tex]K=A\times e^{\frac{-Ea}{RT}}[/tex]

The expression used with catalyst and without catalyst is,

[tex]\frac{K_2}{K_1}=\frac{A\times e^{\frac{-Ea_2}{RT}}}{A\times e^{\frac{-Ea_1}{RT}}}[/tex]

[tex]\frac{K_2}{K_1}=e^{\frac{Ea_1-Ea_2}{RT}}[/tex]

where,

[tex]K_2[/tex] = rate of reaction with catalyst

[tex]K_1[/tex] = rate of reaction without catalyst

[tex]Ea_2[/tex] = activation energy with catalyst  = 23.0 kJ/mol = 23000 J/mol

[tex]Ea_1[/tex] = activation energy without catalyst  = 84.0 kJ/mol = 84000 J/mol

R = gas constant = 8.314 J/mol.K

T = temperature = [tex]25^oC=273+25=298K[/tex]

Now put all the given values in this formula, we get

[tex]\frac{K_2}{K_1}=e^{\frac{(84000-23000)J/mol}{8.314J/mol.K\times 298K}}[/tex]

[tex]\frac{K_2}{K_1}=4.93\times 10^{10}[/tex]

Therefore, the rate constant of the reaction is increased by factor, [tex]4.93\times 10^{10}[/tex]

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