ShmoopTube

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Here’s your Shmoop du jour, brought to you by propane, the movement that advocates for [Window panes outside a building]

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windows.

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Here’s today’s question:

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When propane, a flammable compound commonly used in gas grills, is ignited, it will react

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with oxygen in a combustion reaction.

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The reaction can be seen below: C3H8 + O2 ? CO2 + H2O

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Once this equation is correctly balanced, how many moles of oxygen will be required

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for each mole of propane?

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And here are your potential answers…

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Okay, flex those fingers, crack those knuckles, and practice opening a jar or two, because [Man attempting to open a jar]

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we’re gonna have to balance this whole equation by hand.

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We’re going to release all the carbon in our propane in the form of carbon dioxide. [Carbon dioxide released from propane]

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That means that the carbons contained in carbon dioxide should be equal to the carbons in

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the propane.

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So let’s balance those guys first. [Carbon molecules balancing on a scale]

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Grab your umbrella!

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Or whatever people use to balance on tightropes.

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Okay, so there are three carbons on the left and one on the right, so we’ll need a coefficient

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of 3 in front of that carbon dioxide.

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Now we need to ask a question to our hydrogen atoms: water you doing? [Oxygen smiling with two hydrogen atoms]

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Well, our hydrogen atoms are all busy forming water molecules when the propane is ignited…

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Which means that we need to balance the hydrogens in propane with the hydrogens in water on

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the other side of the equation.

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Because for every propane, there is an equal and opposite con-pane.

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That doesn’t mean anything. [Girl looking at a book]

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Don’t look that up.

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To balance our hydrogens, we observe that there are two hydrogens in water and eight

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in propane, so it’ll take four water molecules to balance the equation.

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But we’re not done!

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No celebratory fist bumps just yet… [Boy offering a fist bump]

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We still have to balance our oxygens.

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On the right side of the equation we have 6 oxygens from carbon dioxide and 4 from water

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for a total of 10.

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On the left, we have two per molecule, so let’s put a five in front of that oxygen

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to balance it out.

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That must mean that our answer is D, since the coefficient in front of our oxygen molecule [Number 5 circled]

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is 5.

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Next time, maybe let’s just stick to charcoal. [Santa jumping down a chimney]

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Or good ol’ firewood.

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Seriously, that propane stuff was way complicated.

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Okay, now it’s celebratory fist bump time.

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Pound it. [Boy offering a fist bump]

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