Question

Posted by Brunette on Sunday, October 14, 2012 at 10:42pm.

Values of the rate constant for the decomposition of N2O5 at four different temperatures are as follows:

T(K) k(s^-1)
658....2.14*10^5
673....3.23*10^5
688....4.81*10^5
703....7.03*10^5

The activation energy is 1.02*10^2 kJ/mol. Calculate the value of the rate constant at 300 K
chemistry - DrBob222, Sunday, October 14, 2012 at 11:23pm
Can't you use the Arrhenius equation?
Use two T values with corresponding k values. One T will be 300 and k at that T will be the unknown.
chemistry - Brunette, Monday, October 15, 2012 at 6:36pm
I keep trying that and it is saying that I have the wrong answer. here is my work:

slope: -1.19*10^4 y-intercept= 30.439

Ea: -(-1.19*10^4 K) *(8.314J/moK)= 9.89*10^4 J/mol

A= e^30.439= 1.65*10^13

(1.65*10^13) e^-(9.89*10^4J/mol/8.314*300 K)= 9.98*10^-5

I keep getting different answers, and each time they are saying it is wrong. Can you tell me where I am going wrong? And am I supposed to convert the Ea into joules/mole?

Answer 1

Yes, Ea goes in with units of J.
You don't need a graph.
ln(k2/k1) = (Ea/R)(1/T1 - 1/T2)
Pick a k1 with T1, then k2 with 300 K for T2 and solve for k2. R is 8.314.

Answer 2

Oh! Thank you! I forgot to pick a second temperature.