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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 253486 times)

Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #675 on: December 28, 2010, 02:34:33 pm »
I think you got it now =]
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Offline blackberry

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #676 on: December 28, 2010, 08:38:37 pm »
i noe ari but im just giving a non-magnified/approximate view of what it wud look like!!! :) :)
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Offline NidZ- Hero

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #677 on: January 02, 2011, 03:40:17 pm »
where do u guys get de edxcel past papers 4rm ASAp plz reply
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Offline blackberry

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #678 on: January 02, 2011, 05:26:19 pm »
i just get it from the edexcel site or from google
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Offline Amii

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #679 on: January 02, 2011, 06:35:55 pm »
Quote from: Nidzzz on January 02, 2011, 03:40:17 pm
where do u guys get de edxcel past papers 4rm ASAp plz reply
https://studentforums.biz/pastpapers/edexcel-new-syllabus-biology-physics-chemistry-pastpapers!!!!!!!/

http://www.freeexampapers.com/past_papers.php?l=Past_Papers/A+Level  - I am getting it "invalid" now - Possibly some problem - Check it again later  ;)

Take care  :D

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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #680 on: January 02, 2011, 07:35:21 pm »
Quote from: Nidzzz on January 02, 2011, 03:40:17 pm
where do u guys get de edxcel past papers 4rm ASAp plz reply

Hey Nidzz ,

as blackberry said I get it from Google , Plus I downloaded the files from FEP in the summer break and so I have them on my USB =]

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #681 on: January 03, 2011, 07:28:50 am »
what does this mean ?! o.0

1. polar covalent where the bonding pair of electrons is  nearer to one atom

2. Dispersion forces

3. Dipole/dipole forces (aka Van Der Waals): between ?+ in one molecule and ?- in another molecule.

Really Confused here , Someone Please help .
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #682 on: January 03, 2011, 09:55:26 am »
Quote from: ~ The Golden Girl  ~ on January 03, 2011, 07:28:50 am
what does this mean ?! o.0

1. polar covalent where the bonding pair of electrons is  nearer to one atom

2. Dispersion forces

3. Dipole/dipole forces (aka Van Der Waals): between ?+ in one molecule and ?- in another molecule.

Really Confused here , Someone Please help .


When you consider Hydrogen Fluoride, for example, the highly electronegative fluorine attracts the bonding electrons to itself such that they stay most of the time on the Fluorine atom. Thus, a dipole-dipole moment is setup with HF becoming a polar molecule.

London Dispersion Forces = Van Der Waals forces.
 
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #683 on: January 03, 2011, 01:01:19 pm »
well then what does a dipole/dipole mean ?
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #684 on: January 03, 2011, 01:10:54 pm »
Quote from: ~ The Golden Girl  ~ on January 03, 2011, 01:01:19 pm
well then what does a dipole/dipole mean ?

Basically in the above example Hydrogen has a deficiency of electrons since they maybe on the Fluoride atom. Thus Hydrogen has a positive dipole (think of it as a slight positive charge).

Fluorine has an excess of electrons and hence a negative dipole.

These are temporary dipoles and may not always exist i.e. they fluctuate in the sense the electrons are constantly moving such that may not always be on the Fluoride atom.
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #685 on: January 03, 2011, 01:14:45 pm »
Quote from: Ari Ben Canaan on January 03, 2011, 01:10:54 pm
Basically in the above example Hydrogen has a deficiency of electrons since they maybe on the Fluoride atom. Thus Hydrogen has a positive dipole (think of it as a slight positive charge).

Fluorine has an excess of electrons and hence a negative dipole.

These are temporary dipoles and may not always exist i.e. they fluctuate in the sense the electrons are constantly moving such that may not always be on the Fluoride atom.

We call it Partially (-vely/+vely )charged .

Thanks Mate =]
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #686 on: January 04, 2011, 08:17:28 pm »
What is the difference between A curly-half arrow and Full curly arrow in reaction mechanism??
Thx
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Offline Amii

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #687 on: January 04, 2011, 08:34:23 pm »
Quote from: ang3l on January 04, 2011, 08:17:28 pm
What is the difference between A curly-half arrow and Full curly arrow in reaction mechanism??
Thx
Hey

A half-headed or fish hook arrow represents the movement of a single electron.

Example -When light in the intiation stage splits a chlorine molecule into chlorine radicals by homolytic fission.

A full-headed curly arrow represents the movement of a pair of electrons.

Check this link out - might help
http://www.chemguide.co.uk/basicorg/conventions/curlies.html
Take care  :D
« Last Edit: January 04, 2011, 08:41:38 pm by Amii »
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #688 on: January 05, 2011, 03:41:08 pm »
Quote from: Amii on January 04, 2011, 08:34:23 pm
Hey

A half-headed or fish hook arrow represents the movement of a single electron.

Example -When light in the intiation stage splits a chlorine molecule into chlorine radicals by homolytic fission.

A full-headed curly arrow represents the movement of a pair of electrons.

Check this link out - might help
http://www.chemguide.co.uk/basicorg/conventions/curlies.html
Take care  :D

Oh thankyou :)

Can anyone do this question for me, Confused a bit

Q: Calculate the enthalpy change for the reaction of propanoic acid to propanal:
CH3CH2COOH + H2 --> CH3CH2CHO + H2O

Givent he following enthalpies of combustion
Propanoic acid: -1527
Hydrogen: -286
Propanal: -1821


Thanks
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #689 on: January 05, 2011, 04:17:12 pm »
Quote from: ang3l on January 05, 2011, 03:41:08 pm
Oh thankyou :)

Can anyone do this question for me, Confused a bit

Q: Calculate the enthalpy change for the reaction of propanoic acid to propanal:
CH3CH2COOH + H2 --> CH3CH2CHO + H2O

Givent he following enthalpies of combustion
Propanoic acid: -1527
Hydrogen: -286
Propanal: -1821

Thanks

Enthalphy change of reaction = reactants - products.

Therefore, (propanoic acid + Hydrogen) - Propanal
              (-1527)+(-286) - (-1821)

Enthalphy change of reaction = +8 kjmol-1
« Last Edit: January 05, 2011, 04:20:20 pm by Amelia »
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