# A level Chemistry help!Watch

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#1
This question:
150cm^3 of SO2 (g) and 100cm^3 O2 react together.
A) State which reactant is in excess.
B) State the volume of SO3 (g) that could form using these quantities.
The answer was oxygen being in excess but I don’t get that because SO2 has a higher volume so shouldn’t that be in excess?
And the answer for b is 150cm^3 which I don’t get either
Thank you so much for the help in advance
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3 weeks ago
#2
You must always consider the balanced equation.
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#3
When balanced, there’s 2 mols of SO2 and one mole of O2 making 2 mols of SO3
Which makes me confused because SO2 has more moles than O2 so shouldn’t that be in excess?
I now get part b when taking the balanced equation in to consideration
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3 weeks ago
#4
(Original post by Iqra_hussain216)
When balanced, there’s 2 mols of SO2 and one mole of O2 making 2 mols of SO3
Which makes me confused because SO2 has more moles than O2 so shouldn’t that be in excess?
I now get part b when taking the balanced equation in to consideration
If 2SO2 + O2 --> 2SO3
This means that you need twice as much SO2 than O2 to react all the O2
As this is not the case oxygen is in excess: you can react all the SO2 and have O2 left over
Last edited by EierVonSatan; 3 weeks ago
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#5
But there’s less oxygen mass wise and mole wise
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#6
That’s what I keep getting confused about
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3 weeks ago
#7
(Original post by Iqra_hussain216)
That’s what I keep getting confused about
So if you wanted to react all the oxygen you would need 200cm3 of SO2 (twice as much). Happy with this?

But you have only 150cm3, so you can't react all the oxygen. Just half that amount - 75cm3.

There is oxygen left over when all the SO2 has been used up. 100-75cm3 = 25cm3

Oxygen is in excess
Last edited by EierVonSatan; 3 weeks ago
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#8
I kind of get it
But if I answered it myself without asking for help I’d most probably not get it
But SO has a volume of 150cm3 so to react with O2 wouldn’t you just need 150cm3 of SO2 in order for that or happen
Sorry if I’m being a nuisance but honestly thank you so much
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3 weeks ago
#9
(Original post by Iqra_hussain216)
I kind of get it
But if I answered it myself without asking for help I’d most probably not get it
But SO2 has a volume of 150cm3 so to react with O2 wouldn’t you just need 150cm3 of SO2 in order for that or happen
Sorry if I’m being a nuisance but honestly thank you so much
No, because the chemical equation says that it is not a 1:1 ratio.

You need two molecules of SO2 to react with every molecule of O2
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#10
Ohhh I get that now
Omg thank you so much 😊 I really appreciate the help
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#11
Omg I get that
Thank you so much again
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