How to speed up chemical reactions (and get a date) - Aaron Sams

2,227,083 views ・ 2012-06-18

TED-Ed


Please double-click on the English subtitles below to play the video.

00:14
Meet our chemist, Harriet.
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She has a chemical reaction that needs to occur more quickly.
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A chemist has some processes at her disposal
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that can help her speed up her reaction,
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and she knows of five ways.
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And to remember them,
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she thinks back to her days as a high school student,
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and the day she got a date for the dance.
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Harriet was in high school, studying between classes.
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She had lost track of time and was going to be late to class.
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Unbeknownst to her,
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Harold, who was just around the corner, was running late, too.
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They both sprinted to class
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and, as it happened, sprinted directly into one another.
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Now, this was no small collision.
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They ran squarely into one another in such a way
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that he knocked the books right out of her hand.
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"I'm sorry," he said. "Let me help you with your books."
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He kindly helped her re-collect her belongings,
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and politely offered to walk her to class.
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And you'll never guess who went together to the dance later that year.
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Yup, those two.
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So as we can see from this example,
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the key to getting a date for the dance is to collide with someone
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and knock the books out of their hands.
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Now, you're probably already aware
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that not all collisions lead to dates for the dance,
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thankfully.
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The collisions must have two important characteristics:
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One, correct orientation that allows books to be knocked from one's hands;
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and two, enough energy to knock the books out.
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Shortly after this incident,
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Harriet decided to tell me, her chemistry teacher, all about it.
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I noticed some interesting parallels
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between her story and chemical reaction rates,
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which happened to be what she was studying in the hallway
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the day of the collision.
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Together, we decided to set out on two missions.
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Harriet wanted to help all chemistry students and chemists
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remember how to speed up the rate of chemical reactions
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and I, being the nice guy that I am,
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decided to make it my mission to help create educational environments
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in which more book-dropping collisions can take place
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to increase future chemists' chances of getting a date for the dance.
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In order to facilitate this improved dance-date-getting process,
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I propose five changes to all schools
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that parallel Harriet's five ways to increase chemical reaction rates.
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First, I propose that we shrink the size of the hallways.
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This will make it more difficult to safely navigate the hallways
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and will cause more collisions than in larger hallways.
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And by increasing the number of collisions,
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we increase the likelihood
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that some of those collisions will have the correct alignment
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and enough energy to create a date to the dance.
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Now, chemically speaking,
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this is equivalent to lowering the volume of a reaction vessel
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or a reaction mixture.
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In doing so, the individual particles are closer together,
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and more collisions will occur.
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More collisions means a greater likelihood
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that collisions with the appropriate energy and configuration will happen.
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Second, I propose increasing the overall population of the school.
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More students equals more collisions.
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By increasing the number of particles available for collision,
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we create an environment where more collisions can take place.
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Third, we must reduce the time allowed between classes --
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heck, let's just cut it in half.
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In doing so, students will need to move more quickly
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to get from one class to the next.
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This increase in velocity will help make sure
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collisions have the appropriate amount of energy necessary
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to ensure book-dropping.
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This is analogous to increasing the temperature of the reaction mixture.
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Higher temperature means particles are moving faster.
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Faster-moving particles means more energy,
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and a greater likelihood of the reaction-causing collision.
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Fourth, students must stop traveling in packs.
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By traveling in packs, the students on the outside of the pack
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insulate those in the middle from undergoing any collisions.
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By splitting up, each student has more area exposed
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that is available for a collision from a passing student.
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When particles travel in packs, the surface area is very small,
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and only the outside particles can collide.
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However, by breaking up the clumps into individual particles,
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the total surface area is increased,
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and each particle has an exposed surface that can react.
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Fifth and finally, we hire a matchmaker.
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Is this colliding and book-dropping too violent?
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Is there an easier way to get a date that requires less initial energy?
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Then a matchmaker will help with this.
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The matchmaker makes it easier for a couple to get together,
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by coordinating the match.
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Our matchmaker is like a catalyst.
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Chemical catalysts function by lowering the activation energy --
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in other words, by lowering the energy required to start a reaction.
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They do this by bringing two particles together
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and orienting them correctly in space so that the two can meet
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at the correct configuration and allow a reaction to take place.
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So, to sum up: if a future chemist wants a date for the dance,
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he must collide with another person
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and knock the books out of their hands.
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And if a chemist wants to make a chemical reaction occur,
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the particles must collide in the correct orientation
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with an appropriate amount of energy.
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And both of these processes can be accelerated,
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using the five methods I've described.
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