An Arrhenius plot (ln k vs. 1/T) for a second order reaction (2A -> C) produced a straight line with a slope of -8.23e+03 K. What is the value of the Arrhenius pre-exponential if k = 4500 M-1 s-1 at 690 K?
The relation between K and T is:
K = A*e^(-Ea/RT)
taking ln on both sides, above expression becomes,
ln K = ln A - Ea/RT
So, slope between ln K and 1/T will have a value of -Ea/R
Here slope = -8.23*10^3
So,
-Ea/R = -8.23*10^3
-Ea/8.314 = -8.23*10^3
Ea = 6.84*10^4 J/mol
we have:
T= 690.0 K
K = 4.5*10^3 M-1.s-1
Ea = 6.84*10^4 J/mol
R = 8.314 J/mol.K
we have below equation to be used:
K = A*e^(-Ea/RT)
4.5*10^3 = A*e^(-68400.0/(8.314*690.0))
4.5*10^3 = A*e^(-11.9233)
4.5*10^3 = A*6.634*10^-6
A = 6.78*10^8 M-1.s-1
Answer: 6.78*10^8 M-1.s-1
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