# AS chemistry help!

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Thread starter 8 years ago
#1
How do I do this question?: "Assuming that all gas volumes are measured under the same conditions and pressure, what is the volume of: Nitrogen forms when 2decimetrecubed ammonia, NH3 , decomposes into its elements ?" Thanks for any help !
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8 years ago
#2
(Original post by oliverh22)
How do I do this question?: "Assuming that all gas volumes are measured under the same conditions and pressure, what is the volume of: Nitrogen forms when 2decimetrecubed ammonia, NH3 , decomposes into its elements ?" Thanks for any help !

.Write out the formula
.Work out the ratios
.And work you way from the n=CV/1000

What exam board are you doing?
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Thread starter 8 years ago
#3
(Original post by lilyobz)
.Write out the formula
.Work out the ratios
.And work you way from the n=CV/1000

What exam board are you doing?
I'm doing Edexcel. I worked out the formula to be 2Nh3 -> N2 + 3H2 and the answer to be: 1dm3. But how can this be? Because does that not mean that 3dm3 of H2 is formed which would mean 4dm3 of gas is formed from only 2dm3? Ahhh I'm so confused! Lol
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8 years ago
#4
(Original post by oliverh22)
I'm doing Edexcel. I worked out the formula to be 2Nh3 -> N2 + 3H2 and the answer to be: 1dm3. But how can this be? Because does that not mean that 3dm3 of H2 is formed which would mean 4dm3 of gas is formed from only 2dm3? Ahhh I'm so confused! Lol
You're doing EDEXCEL FOR CHEMISTERY!?!?!?
I truley pity you ='[, that exam board for chemistry is hell on earth.
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Thread starter 8 years ago
#5
(Original post by lilyobz)
You're doing EDEXCEL FOR CHEMISTERY!?!?!?
I truley pity you ='[, that exam board for chemistry is hell on earth.
Haha, why's that?
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8 years ago
#6
(Original post by lilyobz)
You're doing EDEXCEL FOR CHEMISTERY!?!?!?
I truley pity you ='[, that exam board for chemistry is hell on earth.
not even bro, I heard AQA is more rigorous. My school used to be on AQA but when I started AS Chemistry, our school switched to edexcel so the teachers have said that AQA is slightly more challenging.

Edexcel is tough anyway though.
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8 years ago
#7
(Original post by oliverh22)
I'm doing Edexcel. I worked out the formula to be 2Nh3 -> N2 + 3H2 and the answer to be: 1dm3. But how can this be? Because does that not mean that 3dm3 of H2 is formed which would mean 4dm3 of gas is formed from only 2dm3? Ahhh I'm so confused! Lol
Yes it does mean that. Don't worry there is no contradiction as all gases occupy the same volume for the same number of moles (Avogadro's law)

So if you make gases with fewer atoms in the molecule then you can make more moles of gas and greater volumes.

2NH3 contains two nitrogen atoms and 6 hydrogen atoms

BUT N2 + 3H2 contains exactly the same number of atoms only now they are arranged in smaller molecules. Hence there are more moles in the products.
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Thread starter 8 years ago
#8
(Original post by James A)
not even bro, I heard AQA is more rigorous. My school used to be on AQA but when I started AS Chemistry, our school switched to edexcel so the teachers have said that AQA is slightly more challenging.

Edexcel is tough anyway though.
Anyone do OCR Physics B here?
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8 years ago
#9
(Original post by James A)
not even bro, I heard AQA is more rigorous. My school used to be on AQA but when I started AS Chemistry, our school switched to edexcel so the teachers have said that AQA is slightly more challenging.

Edexcel is tough anyway though.
OCR Chemistry is by far the easiest for chemistry, Its like a sweet summer breeze
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8 years ago
#10
(Original post by oliverh22)
I'm doing Edexcel. I worked out the formula to be 2Nh3 -> N2 + 3H2 and the answer to be: 1dm3. But how can this be? Because does that not mean that 3dm3 of H2 is formed which would mean 4dm3 of gas is formed from only 2dm3? Ahhh I'm so confused! Lol
Gases are funny (not a particularly scientific way to put it ), one mole of any gas (regardless of molecule size / number of component parts) takes up the same volume of space. So when a gas decomposes into more types of molecules, it takes up more volume (or, increases the pressure in the container it is held in), as there are more "types of molecule" each taking up the amount of space in ratio.

Not sure if my wording will help, but it's how I think of it

Also, I was told Salters is horrific for chemistry, and I really enjoy it and don't find it a struggle. Don't be put off by general opinions!
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8 years ago
#11
(Original post by James A)
not even bro, I heard AQA is more rigorous. My school used to be on AQA but when I started AS Chemistry, our school switched to edexcel so the teachers have said that AQA is slightly more challenging.

Edexcel is tough anyway though.
AQA is fine for Chemistry, to be honest.
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Thread starter 8 years ago
#12
(Original post by Fornacite)
Gases are funny (not a particularly scientific way to put it ), one mole of any gas (regardless of molecule size / number of component parts) takes up the same volume of space. So when a gas decomposes into more types of molecules, it takes up more volume (or, increases the pressure in the container it is held in), as there are more "types of molecule" each taking up the amount of space in ratio.

Not sure if my wording will help, but it's how I think of it

Also, I was told Salters is horrific for chemistry, and I really enjoy it and don't find it a struggle. Don't be put off by general opinions!
Ahhhhhhh that would make sense now! cheers! So my answer was correct after all? Haha
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8 years ago
#13
(Original post by Tullia)
AQA is fine for Chemistry, to be honest.
The only difference to be honest is the content, you lot study things like carbon NMR and proton NMR. Edexcel is only proton NMR. I think there might be slight differences in the organic chemistry topics, like the reactions you need to learn for benzene, phenol etc..

But the one thing that can trip people on edexcel is the experiment based questions, some people understand it, some don't.
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Thread starter 8 years ago
#14
(Original post by James A)
The only difference to be honest is the content, you lot study things like carbon NMR and proton NMR. Edexcel is only proton NMR. I think there might be slight differences in the organic chemistry topics, like the reactions you need to learn for benzene, phenol etc..

But the one thing that can trip people on edexcel is the experiment based questions, some people understand it, some don't.
Is there usually a lot of experiment based questions on the exam? (I'm doing Unit 1 in January)
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8 years ago
#15
(Original post by oliverh22)
Ahhhhhhh that would make sense now! cheers! So my answer was correct after all? Haha
Yup!
(But seriously, always ask these questions. Now you know it's right and why, you'll always be able to do those kinda questions )
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Thread starter 8 years ago
#16
(Original post by Fornacite)
Yup!
(But seriously, always ask these questions. Now you know it's right and why, you'll always be able to do those kinda questions )
True dude! Understanding is the key
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8 years ago
#17
wait, gasses at the same volume, isnt that something to do with 24dmcubed??
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Thread starter 8 years ago
#18
(Original post by xxrebeccabexixx)
wait, gasses at the same volume, isnt that something to do with 24dmcubed??
Yes. However that equation isn't necessary for the type of question I was asking about
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8 years ago
#19
(Original post by xxrebeccabexixx)
wait, gasses at the same volume, isnt that something to do with 24dmcubed??
Yup, at standard conditions (Room temperature + 1atm pressure) 1 mole of any gas will take up the volume 24cm^3
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8 years ago
#20
(Original post by oliverh22)
Is there usually a lot of experiment based questions on the exam? (I'm doing Unit 1 in January)
There's a fair chunk of it, yes. To be honest, make sure your thoroughly prepared, go over old past papers, even old specification past papers.

https://eiewebvip.edexcel.org.uk/Pas...s/Default.aspx

Here you will find some old spec edexcel papers (the board was previously called Edexcel Nuffield).

I got an A in unit 1, scraped it.
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