ShmoopTube

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And here’s your Shmoop du jour, brought to you by reaction rate.

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Hey, think fast! …Ooh, that’s gotta hurt. [Boy strikes a ball with a bat and ball hits man in face]

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Sorry…

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Here’s today’s problem:

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The reaction: A + B yields C was run three different times, and each time, the concentrations

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of the reactants were altered.

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The reaction rate was also measured each time the reaction was run, as shown in the table.

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What is the experimental rate law for this reaction? [Table of experiment measurements]

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And here are your potential answers.

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To answer this question, we’ll need to examine the experimental data and deduce the appropriate

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rate law for this reaction. [Doctor with a zombie-looking man on a table]

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The reactants here are species A and B. In the three experiments shown in the table,

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the initial concentrations of A and B are varied.

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Because everyone is special in their own way. [Woman hugging a young boy]

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Anyway, between experiments 1 and 3, the initial concentration of A is doubled while the initial

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concentration of B stays the same.

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We can use these two data points to find out how the rate depends on the concentration [Rate swinging and A grabs it]

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of species A without worrying about species B.

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So, what is the dependence on A? [A and B sitting on a couch]

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When the initial concentration of A is doubled, the rate stays the same, so it doesn’t depend

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on A at all.

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Kind of like how your parents don’t depend on you to do the dishes anymore. [Girl sitting on a couch with a pizza]

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Yeah, we know, you'd get to them "in a minute".

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Whatever you say.

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So between experiments 1 and 2, the initial concentration of B is doubled, while the initial

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concentration of A stays the same.

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With these two points, we can find how the rate depends on species B.

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When the concentration of B is doubled, the rate increases by four times. [B increases in size and a hand holding 4 fingers appears]

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That means the rate depends on B squared.

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That's not quite like us… when our concentration is doubled, we make it through class without

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falling asleep.

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We know.

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Not all heroes wear capes. [People staying awake in a classroom]

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Anyway, now we know that the rate depends on the concentration of B squared, but it

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doesn’t depend on A at all.

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Looking at our answers, choice (A) fits the bill, as all the others include some dependence

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on species A. So choice (A) is the right answer.

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Now it’s time to get those dishes done. [A collection of dirty dishes]

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Hey, where are you going?

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Oh, brother.

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Seriously, maybe your brother will do them instead. [Brother and sister run away]

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