Question from TPR Hyperlearning Gen Chem, Passage 49

[farnell]

"Considering that chlorine can catalyze the destruction of 03 in the stratosphere, which one of the following statements must NOT be true?"

A. Chlorine lowers the Ea of the rate-determining step.
B. Chlorine does not affect the overall energy released during the destruction of ozone.
C. The concentration of 03 in the stratosphere is greater than it should be at equilibrium concentrations.
D. None of the above.

A and B are definitely true, so A and B are wrong. However, I believed C to not be true because a catalyst does not affect the final concentrations of reactants or products at equilibrium, only the rate at which that reaction reaches equilibrium. So I put down C.

The back of the book says D. Can anyone help as to how C might be true?

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[ohitsthatguy]

That is true that the catalyst will not affect the final concentration. Keeping this in mind, it is possible for the ozone to be in greater quantities than equilibrium. The chlorine catalyzing the destruction will produce the same final amount as if no catalyst was used, it will just be at a faster rate. Also, because the system is not at equilibrium, it would make sense that a catalyst can be used on it to achieve equilibrium like we said, at a faster rate. (Just the fact that we have a catalyst does not affect that starting amount of ozone)

Hope this makes sense!

 

[farnell]

That is true that the catalyst will not affect the final concentration. Keeping this in mind, it is possible for the ozone to be in greater quantities than equilibrium. The chlorine catalyzing the destruction will produce the same final amount as if no catalyst was used, it will just be at a faster rate. Also, because the system is not at equilibrium, it would make sense that a catalyst can be used on it to achieve equilibrium like we said, at a faster rate. (Just the fact that we have a catalyst does not affect that starting amount of ozone)

Hope this makes sense!

Ah, that makes perfect sense. I think I was reading choice C as, "The concentration of ozone at equilibrium is greater," though it was actually saying, "The concentration of ozone is greater before equilibrium is reached," which makes sense.

Thank you!!

 

[ohitsthatguy]

Anytime, glad I could help