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# lnk = lnA - Ea / RT question

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1. Please can someone check if this is right?

k = 6.51 x 10^-3 mol-1dm3
T = 300K
A = 2.57 x 10^10 mol-1dm3
R = 8.31 JK-1mol-1

Using lnk = lnA - Ea / RT find Ea in kJmol-1

I did:

ln6.51 x 10^-3 = ln2.57 x 10^10 - Ea / 8.31 x 300
-12550.79... = ln2.57 x 10^10 - Ea
Ea = ln2.57 x 10^10 + 12550.79...
Ea = 12574.768... Jmol-1
Ea = 12.6 kJmol-1 (3.s.f)
2. Anyone?
3. (Original post by kiiten)
Please can someone check if this is right?

k = 6.51 x 10^-3 mol-1dm3
T = 300K
A = 2.57 x 10^10 mol-1dm3
R = 8.31 JK-1mol-1

Using lnk = lnA - Ea / RT find Ea in kJmol-1

I did:

ln6.51 x 10^-3 = ln2.57 x 10^10 - Ea / 8.31 x 300
-12550.79... = ln2.57 x 10^10 - Ea
Ea = ln2.57 x 10^10 + 12550.79...
Ea = 12574.768... Jmol-1
Ea = 12.6 kJmol-1 (3.s.f)
I make it 72.3 kJ
4. (Original post by charco)
I make it 72.3 kJ
How? What did you do?
5. I got 72.3kj/mol too. Double check your rearranging. To make it easier, rearrange before you put your numbers in.
6. (Original post by typicalvirgo)
I got 72.3kj/mol too. Double check your rearranging. To make it easier, rearrange before you put your numbers in.
-1 ((lnk x RT) - lnA)
7. I also got 73.2kj/mol. Show us the steps of your rearranging.
8. (Original post by spidle)
I also got 73.2kj/mol. Show us the steps of your rearranging.
ln6.51 x 10^-3 = ln2.57 x 10^10 - Ea / 8.31 x 300
-12550.79... = ln2.57 x 10^10 - Ea
Ea = ln2.57 x 10^10 + 12550.79...
Ea = 12574.768... Jmol-1
Ea = 12.6 kJmol-1 (3.s.f)
9. (Original post by kiiten)
ln6.51 x 10^-3 = ln2.57 x 10^10 - Ea / 8.31 x 300
-12550.79... = ln2.57 x 10^10 - Ea
Ea = ln2.57 x 10^10 + 12550.79...
Ea = 12574.768... Jmol-1
Ea = 12.6 kJmol-1 (3.s.f)
In step 2, you forgot to times In(2.57 x 10^10) by (8.31x300).
10. (Original post by kiiten)
ln6.51 x 10^-3 = ln2.57 x 10^10 - Ea / 8.31 x 300
-12550.79... = ln2.57 x 10^10 - Ea
You went wrong at this part. You multiplied the whole left side by RT when it is only EA/RT on the right hand side, not (lnA-Ea/RT) but rather lnA-(Ea/RT).
11. (Original post by spidle)
You went wrong at this part. You multiplied the whole left side by RT when it is only EA/RT on the right hand side, not (lnA-Ea/RT) but rather lnA-(Ea/RT).
Oh so would it be:

RT (lnA - lnk) = Ea
12. Yeah that's right. It should give you 72307J/mol so 72.3kJ/mol.

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