AQA GCSE Chemistry C2/C3 May 15th 2014 Watch

famzyjaanxx
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#61
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when finding the rate of reaction why do we need a high resolution balance? (2 marks)
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Iz279
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Can anyone help me out with these? I'm doing some C3 past papers and I can't work out how to do them - I've looked at the mark schemes but I don't get how you work them out! Thanks in advance 😘Name:  ImageUploadedByStudent Room1400098796.724435.jpg
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chronicmusic
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(Original post by Student 977)
When the products of a reaction are able to either split up or react to create the original reactants.
Bingo!
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Student 977
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(Original post by chronicmusic)
If the products line is lower than the reactants line (the energy of the products is lower than the energy of the reactants), the reaction is exothermic. It's the opposite for endothermic.

My question:

When do reversible reactions occur?
When the products from a reaction are able to either split up or react to form the original reactants.
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chronicmusic
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(Original post by Kevin Paul Beale)
Describe the process of making ammonia. (4 marks)

Why do the scientists choose not to use the pressure that produces the highest rate of reaction? (2 marks)
To make ammonia you would use the haber process. You will need nitrogen and hydrogen. In the Haber process, nitrogen and hydrogen react together under a high temperature (about 450°C) and a high pressure. An iron catalyst can be used to increase the rate of reaction.

I don't know the second one
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famzyjaanxx
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(Original post by Kevin Paul Beale)
Describe the process of making ammonia. (4 marks)

Why do the scientists choose not to use the pressure that produces the highest rate of reaction? (2 marks)
1) nitrogen (from the air) and hydrogen (from hydrocarbons or electrolysis of water) is put into a reaction vessel. the reaction vessel has trays of iron as a catalyst to make the reaction speed up. the nitrogen and hydrogen react to produce ammonia. ammonia is a gas at this stage so its cooled in a condenser and then liquefied and removed. the conditions are 450 degrees Celsius and 200 atmospheres
2) scientists don't choose high pressures as they need stronger vessel material high pressure would mean stronger expensive material so not profitable.
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Hamzah313
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(Original post by majmuh24)
Exothermic - Reactants have more energy than products

Endothermic - Reactants have less energy than products

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Is that C2 or C3?
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chronicmusic
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(Original post by Iz279)
Can anyone help me out with these? I'm doing some C3 past papers and I can't work out how to do them - I've looked at the mark schemes but I don't get how you work them out! Thanks in advance ������Name:  ImageUploadedByStudent Room1400098796.724435.jpg
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This may help you better than the other explanation:
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Iz279
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Ok thanks for the help! The only thing I still don't understand is why you divide by 1000? Am I just being really thick?


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interstitial
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(Original post by Hamzah313)
Is that C2 or C3?
C2 I think, not sure man

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chronicmusic
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(Original post by AlphaNick)
woo I got it right :P
Good job!
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tevagx51
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(Original post by chronicmusic)
This may help you better than the other explanation:
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really confused lool, where does the 0.025 come from ?

anybody have any suggestions on which areas to prioritise on for both exams as i only really started revising now!
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chronicmusic
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(Original post by Iz279)
Ok thanks for the help! The only thing I still don't understand is why you divide by 1000? Am I just being really thick?


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30.5 is in cm3, however the concentration of moles is 0.5 per decimetre - you need to convert cm3 to decimetres (i.e. divide by 1000)
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interstitial
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(Original post by tevagx51)
really confused lool, where does the 0.025 come from ?

anybody have any suggestions on which areas to prioritise on for both exams as i only really started revising now!
You've got cm^3.

10cm=1dm, so 10*10*10cm^3=1dm^3. This means that there are 1000cm^3 in 1 dm^3, so you divide by 1000 to get everything into dm^3.

Then just rearrange n=c*V.

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Excuse Me!
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(Original post by Kevin Paul Beale)
Describe the process of making ammonia. (4 marks)

Why do the scientists choose not to use the pressure that produces the highest rate of reaction? (2 marks)
1. Nitrogen and hydrogen are heated at around 450 degrees Celsius with a pressure of about 200 atmospheres. An iron catalyst is used to lower the activation energy. 2. A high pressure would require specialist machinery that would be expensive so would lessen the profits made.
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mickel_w
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For those of you doing all 3 units, which ones would you say are the hardest for each subject?
I only do additional, and I reckon C2 is easier than C1, but both B2 and P2 are slightly harder than the core.
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famzyjaanxx
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(Original post by mickel_w)
For those of you doing all 3 units, which ones would you say are the hardest for each subject?
I only do additional, and I reckon C2 is easier than C1, but both B2 and P2 are slightly harder than the core.
i find them both okay i can get slip up on both but if i had to make a choice i would say c2 because theres more content to learn whereas c3 its not alot
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notevensoph
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Nanoparticles and carbon nanotubes i feel like is going to come up, does anyone know how much in depth we are supposed to know?
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famzyjaanxx
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(Original post by AlphaNick)
I'd say difficulty goes (easiest to hardest):
C1, C3, C2
same i found c3 easier
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famzyjaanxx
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(Original post by Sophsha)
Nanoparticles and carbon nanotubes i feel like is going to come up, does anyone know how much in depth we are supposed to know?
yeah i have that feeling too
just learn the advantages and disadvantages at least 5 for each then learn about the structure and the definition of nanoparticles
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