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Chemistry: Activation Energy (Arrhenius equation) 
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#1
Feb907, 02:57 PM

P: 3

1. The problem statement, all variables and given/known data
A certain reaction, with an activation energe of 64.5 kJ/mole, is run at 25.0'C (degree Celsius) and its rate is measured. How many times faster would this reaction be if it were run at 50.0'C (degree Celsius)? 2. Relevant equations I think: (Arrhenius equation) ln(k1/k2) = Ea/R (1/T2  1/T1) R = 8.314 J/mole*K 3. The attempt at a solution I don't know where to start. Only Ea = 64.5 kJ/mole, 1 temperature = 25.0'C and R (8.314 J/mole*K) are given. I don't know where to get the other numbers to plug in the equation. 


#2
Feb907, 03:04 PM

P: 147

remember, you also have a T2 (50degC). You don't necessarily need to solve for the individual k values, just figure out a relationship between them.



#3
Feb1107, 01:36 PM

P: 16

i just did this problem on my homework
we have ln( k2/k1 ) = (Ea/R) * (1/T1  1/T2) where k is the reaction constant, Ea is activation energy, R is gas constant, T is temperature what are we solving for? well we want to see how k changes. we rearrange the equation: [antilog of both sides] k2/k1 = antilog[ (Ea/R) * (1/T1  1/T2) ] [multiple by k1 on each side] k2 = k1 * antilog[ (Ea/R) * (1/T1  1/T2) ] [antilog(x) just means e^(x)] k2 = k1 * e^[ (Ea/R) * (1/T1  1/T2) ] here we go! we wanted to see how k changes right? the new k (k2) value equals the old k (k1) value times e^[ (Ea/R) * (1/T1  1/T2) ] the reason it was tricky is because we weren't solving for a variable, we just wanted to see how k would change when the temperature changed so the answer is: when the temperature is 50C, it is ((( e^[ (Ea/R) * (1/T1  1/T2) ] ))) times faster than when it is at 25C just plug and chug: Ea = 64.5kj/mol = 64500 j/mol T1 = 25*C = 298K T2 = 50*C = 323K R = 8.314 J/mole*K 


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