July 16, 2019, 12:46:51 AM
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Topic: Photochemistry quantum yield  (Read 620 times)

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Offline electrogeek

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Photochemistry quantum yield
« on: February 18, 2019, 08:53:20 AM »
Hello,

I'm stuck on a question on photochemical reactions. I've attached a screenshot of it below, and I think I have worked out the first part of the question which asks for an expression for the quantum yield of the reaction which Ive written at the bottom of the screenshot. But I don't know how to show that the data is consistent with the scheme.

I first thought about finding an equation based of the quantum yield which shows a linear relationship by plotting the reciprocal of the quantum yield against concentration, but this didn't give me a straight line. However, I do get a straight line if I do the reciprocal of the quantum yield against the reciprocal of the concentration, but I can’t get my quantum yield expression to do this (i.e: I can't get an equation of the form y = mx + c with 'y' as the reciprocal of the quantum yield and 'x' as the reciprocal of concentration).

I was wondering how I could go about proving the data is consistent with the data. Any help will be greatly appreciated. :)

Offline mjc123

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Re: Photochemistry quantum yield
« Reply #1 on: February 18, 2019, 12:46:20 PM »
Look again at your expression for Φ. Have you missed anything out? When it's correct, it will give a linear relationship between 1/Φ and 1/[ B].

Offline electrogeek

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Re: Photochemistry quantum yield
« Reply #2 on: February 18, 2019, 01:46:24 PM »
Hello,

I've attached a picture of my workings for the expression. I know that I abs is the same as J * [A] but I'm not sure where else the concentration of B appears because it is only in the last equation...
« Last Edit: February 18, 2019, 01:59:48 PM by electrogeek »

Offline mjc123

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Re: Photochemistry quantum yield
« Reply #3 on: February 19, 2019, 04:29:46 AM »
You went wrong in the first line. What is the rate of the reaction?

Offline electrogeek

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Re: Photochemistry quantum yield
« Reply #4 on: February 19, 2019, 06:07:35 AM »
Ah... Thank you very much - got the right relationship now. :)

Offline mjc123

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Re: Photochemistry quantum yield
« Reply #5 on: February 19, 2019, 08:27:56 AM »
It should have been obvious that k2 can't have the same units as k1, so your Φ couldn't be a dimensionless number.

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