Register to reply

Chemistry: Activation Energy (Arrhenius equation)

by lonelyassassin
Tags: activation, arrhenius, chemistry, energy, equation
Share this thread:
Feb9-07, 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.
Phys.Org News Partner Science news on
Bees able to spot which flowers offer best rewards before landing
Classic Lewis Carroll character inspires new ecological model
When cooperation counts: Researchers find sperm benefit from grouping together in mice
Feb9-07, 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.
Feb11-07, 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

Register to reply

Related Discussions
Arrhenius equation (chemistry) Biology, Chemistry & Other Homework 4
Finding Activation Energy From Arrhenius Plot Biology, Chemistry & Other Homework 3
Gauche Isomerism/Arrhenius Equation Questions Biology, Chemistry & Other Homework 1
Arrhenius equation Biology, Chemistry & Other Homework 5
Arrhenius equations; A2 Chemistry coursework Chemistry 3