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March 29, 2024, 10:37:11 am

Author Topic: Chemistry Question Help!!  (Read 803 times)  Share 

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JamieLeaf

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Chemistry Question Help!!
« on: February 20, 2019, 12:45:15 am »
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Hey Guys,
I have read through the solution for this question but I still don't know how to work it out. The question is: 100ml of gaseous hydrocarbon is mixed with 500 ml of oxygen at 20 degrees celsius and 1 atmosphere pressure and sparked. At the end of the reaction the gaseous mixture is returned to its original temperature and pressure. The final mixture consists of 300ml of carbon dioxide and 100 ml of oxygen. The molecular formula of the hydrocarbon is:

A) C2H4
B) C3H4
C) C3H6
D) C3H8

peter.g15

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Re: Chemistry Question Help!!
« Reply #1 on: February 20, 2019, 12:14:34 pm »
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Hey Guys,
I have read through the solution for this question but I still don't know how to work it out. The question is: 100ml of gaseous hydrocarbon is mixed with 500 ml of oxygen at 20 degrees celsius and 1 atmosphere pressure and sparked. At the end of the reaction the gaseous mixture is returned to its original temperature and pressure. The final mixture consists of 300ml of carbon dioxide and 100 ml of oxygen. The molecular formula of the hydrocarbon is:

A) C2H4
B) C3H4
C) C3H6
D) C3H8

Answer is B?

The most important thing to notice in this question is that the start and end reaction are at the same temperature and pressure. This makes our question a lot simpler because it means we can essentially rule this out in our calculations. Therefore, that means that the volume must be the same at the start and finish (i.e. 600mL). This gives us the following compositions:

START
- 100mL Hydrocarbon
- 500mL Oxygen
END
- 300mL Carbon Dioxide
- 100mL Oxygen
- 200mL Water

We can use these in simple mole ratios since we have eliminated the temperature and volume from our question. Therefore, we get:

x (hydrocarbon) + 5O2 --> 3CO2 + O2 + 2H20

Looking at this, the oxygen is already balanced (as it should be - 10 on each side). This leaves carbon and hydrogen. On the products side, we have 3 carbons and 4 hydrogens that need to be accounted for. Therefore, the molecular formula of it should be C3H4.

Hope that's correct and the explanation makes sense, if not, let me know and i'll try explain it in another way :)
2019 - 23: Bachelor of Medical Science and Doctor of Medicine @ Monash University

JamieLeaf

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Re: Chemistry Question Help!!
« Reply #2 on: February 20, 2019, 08:23:23 pm »
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Yep B is correct! Thanks Peter