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You know how sometimes[br]you go to bake a cake

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but your bananas have all gone rotten,

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your utensils have rusted,

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you trip and pour all of your baking soda[br]into the vinegar jug,

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and then your oven explodes?

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My friend, you and your chemical reactions[br]have fallen victim to enthalpy and entropy

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and, boy, are they forces [br]to be reckoned with.

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Now, your reactants are all products.

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So, what are these "E" words,[br]and what's their big idea?

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Let's start with enthalpy,

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an increase or decrease of energy[br]during a chemical reaction.

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Every molecule has a certain amount[br]of chemical potential energy

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stored within the bonds between its atoms.

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Chemicals with more energy [br]are less stable,

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and thus, more likely to react.

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Let's visualize the energy flow [br]in a reaction,

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the combustion of hydrogen and oxygen,[br]by playing a round of crazy golf.

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Our goal is to get a ball, the reactant,[br]up a small rise

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and down the other much steeper slope.

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Where the hill goes up,[br]we need to add energy to the ball,

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and where it goes down, the ball releases[br]energy into its surroundings.

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The hole represents the product,[br]or result of the reaction.

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When the reaction period ends,[br]the ball is inside the hole,

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and we have our product: water.

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This, like when our oven exploded,[br]is an exothermic reaction,

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meaning that the chemical's final energy[br]is less than its starting energy,

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and the difference has been added[br]to the surrounding environment

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as light and heat.

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We can also play out[br]the opposite type of reaction,

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an endothermic reaction,

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where the final energy is greater [br]than the starting energy.

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That's what we were trying [br]to achieve by baking our cake.

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The added heat from the oven would [br]change the chemical structure

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of the proteins in the eggs[br]and various compounds in the butter.

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So that's enthalpy.

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As you might suspect,

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exothermic reactions are more likely [br]to happen than endothermic ones

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because they require less energy to occur.

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But there's another independent factor[br]that can make reactions happen:

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entropy.

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Entropy measures a chemical's randomness.

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Here's an enormous pyramid of golf balls.

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Its ordered structure [br]means it has low entropy.

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However, when it collapses, [br]we have chaos everywhere,

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balls bouncing high and wide.

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So much so that some [br]even go over the hill.

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This shift to instability, [br]or higher entropy,

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can allow reactions to happen.

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As with the golf balls, [br]in actual chemicals

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this transition from structure to disorder[br]gets some reactants past the hump

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and lets them start a reaction.

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You can see both enthalpy[br]and entropy at play

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when you go to light [br]a campfire to cook dinner.

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Your match adds enough energy

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to activate the exothermic reaction[br]of combustion,

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converting the high-energy [br]combustible material in the wood

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to lower energy carbon dioxide and water.

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Entropy also increases[br]and helps the reaction along

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because the neat, organized log of wood

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is now converted into randomly moving[br]water vapor and carbon dioxide.

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The energy shed by this [br]exothermic reaction

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powers the endothermic reaction[br]of cooking your dinner.

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Bon appétit!