ShmoopTube

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Here’s your Shmoop du jour, brought to you by decomposition, like when you burn your [Banana going rotten]

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lab notes at the end of the year. [Kid burning his notebook]

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Here’s today’s question:

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What is the total volume of gas formed at STP from the decomposition of 1.0 mole of

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ammonium nitrate, NH4NO3, with the help of a catalyst?

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The reaction is as shown on the screen. [The formula appears]

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And here are your potential answers: Wait?

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Catalyst?

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Where’s the catalyst? [Cat holding a piece of paper that says list]

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Why would they mention a catalyst and not give us any information about the catalyst? [Scientist picking up different coloured liquids looking confused]

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Or, well, it’s a trick question.

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The catalyst, or lack thereof, doesn’t affect the answer at all people. [Catalyst looking unhappy]

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A catalyst just speeds up a reaction by lowering the activation energy.

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It doesn’t change the extent of the reaction.

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That uncool distraction aside, what the question is really asking is how much gas stuff is [Gas coming out of a flask]

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formed in the reaction. [The flask looks embarrassed]

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Anytime you’re asked how much stuff there is, your immediate thought should be “what

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is that in moles?” [A mole lying on a scale]

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And then your next thought should be, “when’s lunch?” [Guy holds his rumbling stomach]

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So how many moles of gas are formed in the reaction?

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We know from the equation that for every 2 moles of ammonium nitrate we put in, we get

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2 moles of nitrogen gas and 1 mole of oxygen gas out. [The products are highlighted]

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We don’t care about the water because it’s a liquid, and the question is all about gas. [Water looks sad and the gas looks happy]

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So since we’re only putting 1 mole of ammonium nitrate in, we’ll get half of what we would

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from 2 moles, which means 1 mole of nitrogen gas and 0.5 moles oxygen gas for a total of

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1.5 moles of gas.

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But put on the brakes, we’re not done yet. [Car brakes quickly]

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The question asked for volume.

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So how are we going to figure out volume if we can’t just pick up the remote and change [Woman shaking a flask at the TV]

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it?

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Well, the question specified that the conditions are “STP.”

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Unfortunately, that doesn’t stand for “super tiny puppy.” [A puppy small enough to fit in the palm of a hand]

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STP is Standard Temperature and Pressure.

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You should know going into your test that one mole of gas occupies 22.4 liters at STP.

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So we multiply 22.4 by the 1.5 moles of gas we have to get 33.6 Liters of gas.

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Which is actually 34 because of the whole weird science magic of significant figures. [Guy holding a book of significant figures and smiling]

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We don’t even have time to get into that right now.

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So that means that D is the correct answer.

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Now where was that remote? [Woman finds the TV remote]

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We heard the super tiny puppy bowl was on. [Tiny puppies playing football]

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