cakefreak
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Hey,
So I'm a tad confused about what a mechanism is, I know it is the sequence of steps showing the path taken by electrons in a reaction but can someone please give me some examples? Thanks
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lala12
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(Original post by cakefreak)
Hey,
So I'm a tad confused about what a mechanism is, I know it is the sequence of steps showing the path taken by electrons in a reaction but can someone please give me some examples? Thanks
There are lots of examples of mechanisms is science, like breathing mechanism in biology. I think you're interested in chemistry judging by your reference to "electron". Some examples are free radical substitution, nucleophilic attraction etc.

Free radical substitution involves three steps, initiation, propagation and termination. For AQA AS you only need to know it for chlorine and bromine I think. So basically, due to UV light, the CL2 molecules split up, become free radicals so are very reactive and they react with other radicals in the surroundings etc and it goes on until they can't do that any more.

Sorry for waffling, but i hope you get some kind of idea :P
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cakefreak
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(Original post by lala12)
There are lots of examples of mechanisms is science, like breathing mechanism in biology. I think you're interested in chemistry judging by your reference to "electron". Some examples are free radical substitution, nucleophilic attraction etc.

Free radical substitution involves three steps, initiation, propagation and termination. For AQA AS you only need to know it for chlorine and bromine I think. So basically, due to UV light, the CL2 molecules split up, become free radicals so are very reactive and they react with other radicals in the surroundings etc and it goes on until they can't do that any more.

Sorry for waffling, but i hope you get some kind of idea :P
Thanks what would be the mechanism for the dehydration of ethanol to form ethene? I can't seem to find it in the book
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cakefreak
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Oh my I clearly can't see just read it says elimination, sorry for wasting your time
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thegodofgod
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(Original post by cakefreak)
Oh my I clearly can't see just read it says elimination, sorry for wasting your time
Elimination

Conditions: conc H2SO4 or conc H3PO4 catalyst, 170oC

http://www.chemguide.co.uk/mechanism...hanol.html#top
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cakefreak
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(Original post by thegodofgod)
Elimination

Conditions: conc H2SO4 or conc H3PO4 catalyst, 170oC

http://www.chemguide.co.uk/mechanism...hanol.html#top
Thanks I'm a little stuck on this other question at the moment concerning Le Chatlier's Principle

When Bismuth chloride is added to water, a reaction occurs and a white precipitate forms. The following equilibrium is set up

BiCl3 (aq) +H2O equilibrium arrow BiOCl (s) +2HCl (aq)

What would be the effect on the amount of precipitate formed if sodium hydroxide is added to the mixture, explain your answer?

The thing that's puzzling me here is that the question's asking me what would happen if I was to add something that isn't in the reaction ? I know that if something that was already in the equation was added then the yield would increase on the other side of the equation but what would happen here? Thanks in advance
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thegodofgod
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(Original post by cakefreak)
Thanks I'm a little stuck on this other question at the moment concerning Le Chatlier's Principle

When Bismuth chloride is added to water, a reaction occurs and a white precipitate forms. The following equilibrium is set up

BiCl3 (aq) +H2O equilibrium arrow BiOCl (s) +2HCl (aq)

What would be the effect on the amount of precipitate formed if sodium hydroxide is added to the mixture, explain your answer?

The thing that's puzzling me here is that the question's asking me what would happen if I was to add something that isn't in the reaction ? I know that if something that was already in the equation was added then the yield would increase on the other side of the equation but what would happen here? Thanks in advance
Okay, now, NaOH is a base. It reacts with acids, and produces a salt and water. So, which acid will it react with in this case, what will be the products, and how will this affect the equilibrium?
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cakefreak
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It will react with 2HCL (hydrochloric acid) which means it will make salt and water and this will increase the yield on the left hand side of the equation meaning the equilibrium will be shifted there?
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cakefreak
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(Original post by thegodofgod)
Okay, now, NaOH is a base. It reacts with acids, and produces a salt and water. So, which acid will it react with in this case, what will be the products, and how will this affect the equilibrium?
It will react with 2HCL (hydrochloric acid) which means it will make salt and water and this will increase the yield on the left hand side of the equation meaning the equilibrium will be shifted there?
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thegodofgod
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(Original post by cakefreak)
It will react with 2HCL (hydrochloric acid) which means it will make salt and water and this will increase the yield on the left hand side of the equation meaning the equilibrium will be shifted there?
No, but close

Water will be made, as you will have NaOH + HCl --> NaCl + H2O, but since you have more water, the equilibrium position will shift to the right, as Le Chatelier's principle says that the system tries to oppose a change. Therefore, more products will be made.

However, you'll also get more HCl being produced (see above), so that the equilibrium would shift to the left, so that less HCl is produced.

Therefore, there will be no change overall.
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cakefreak
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(Original post by thegodofgod)
No, but close

Water will be made, as you will have NaOH + HCl --> NaCl + H2O, but since you have more water, the equilibrium position will shift to the right, as Le Chatelier's principle says that the system tries to oppose a change. Therefore, more products will be made.

However, you'll also get more HCl being produced (see above), so that the equilibrium would shift to the left, so that less HCl is produced.

Therefore, there will be no change overall.
Sorry I thought that HCL is reacting to form NaCl and H2O so how is it being produced?
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thegodofgod
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(Original post by cakefreak)
Sorry I thought that HCL is reacting to form NaCl and H2O so how is it being produced?
Woops - sorry, ignore the last part - only read the first paragraph about the water. Ignore the rest - I made a stupid, RTFQ mistake
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cakefreak
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(Original post by thegodofgod)
Woops - sorry, ignore the last part - only read the first paragraph about the water. Ignore the rest - I made a stupid, RTFQ mistake
Ahh I see so basically more water is made and therefore equilibrium will shift to opposite side which is the right in order to use up that water Thanks xx
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cakefreak
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(Original post by thegodofgod)
Woops - sorry, ignore the last part - only read the first paragraph about the water. Ignore the rest - I made a stupid, RTFQ mistake
Also, would you be able to give me some tips on the evaluative tasks. Is there no website or book that could help me practice how science works stuff? Thanks in advance x
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thegodofgod
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(Original post by cakefreak)
Ahh I see so basically more water is made and therefore equilibrium will shift to opposite side which is the right in order to use up that water Thanks xx
Yeah :yy:

(Original post by cakefreak)
Also, would you be able to give me some tips on the evaluative tasks. Is there no website or book that could help me practice how science works stuff? Thanks in advance x
Do you have any specific questions?
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cakefreak
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(Original post by thegodofgod)
Yeah :yy:



Do you have any specific questions?
Thanks What increases reliability?
What increases accuracy? I need as much different answers as possible because last time they gave like three markers for reliability :L
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ChemistryJedi
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If the experiment can be repeated by others in similar or the same conditions.
If the experiment produces the same or similar results in these conditions.
If the steps taken to perform the experiment are correct (or the experiment works)
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