Gen Chem Q

[purplepanda]

Two reactions with different activation energies have the same rate at room temperature. Which statement correctly describes the rates of these two reactions at the same higher temperature.

a.) The reaction with the larger activation energy will be faster. (Right)
b.) The reaction with the smaller activation energy will be faster.

How?

If you do Arrhenius equation:

Increase the EA to say 500...then k goes to zero. Smaller k means smaller reaction rate.

Put the EA at 5 and k is a small number greater than zero. So the reaction rate is higher than the larger Ea.

Also, just from common sense it seems that a lower activation energy would make any reaction a faster reaction. Please help me, thank you!

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[miedvied]

R1 = R2
R1 = K1A
R2 = K2B

Where K2 = .5K1, and B = 2A.

If we double our Ks...
R1* = 2K1A = 2K1A
R2* = 2K2B = 2(.5K1)(2A) = K14A

As you can see, higher Ea means lower K, in order to start with equal reaction rates. As temp increases, and K increases (say, doubles), both Ks will double - however, the higher Ea species will still have the larger concentration!

Your intuition was *spot on*, you just overlooked the fact that one species had a higher concentration.

Edit: I made a mistake in my math; the two results should still have come out to equal rates. I do not see the answer to your problem; my apologies, and I hope someone else can contribute the correct explanation.