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SL/HL Chemistry Question (Please Help!)

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If you could please help explain the process of how to solve this question, that would be greatly appreciated :)

 

1. Butane lighters work by the release and combustion of pressurized butane. 

 

2C4H10+13O2=8CO2+10H2O

 

Determine the limiting reagent in the following reaction.

 

a) 20 molecules of C4H10 and 100 molecules of O2. 

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Well basically I think of it as working on ratios. To find the number of moles use the formula: no. of moles = number of molecules N divided by L (Avogadro's constant which is 6.02 x 10^23).
So, you've been given 3.32 x 10^-23 moles of butane.

Doing the same for oxygen you get 1.66 x 10^-22 moles

Back to the concept of ratios, you would need 2.16 x 10^-22 moles of oxygen in order to react with 3.32 x 10^-23 moles of butane. I did this by multiplying (3.32 x 10^-23) by 6.5

Hence, you don't have enough oxygen and so it's your limiting reagent!

I hope this is correct because if it's not, I'm screwed for finals lol.

 

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A slightly easier way of thinking about it is to look at the ratio of C4H10 to O2, which is 2:13 or 1:6.5

So 20 molecules of C4H10 needs (6.5x20) = 130 molecules of O2 to react completely.

So O2 is the limiting reactant.

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