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AS Chemistry- helping each other out!

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Original post by xMillnsy
Can someone describe/ show me the different boltzmann distribution graph for temperature, pressure and catalyst? Thanks


http://www.chemguide.co.uk/physical/basicrates/temperature.html
http://www.chemguide.co.uk/physical/basicrates/catalyst.html
Original post by C0balt

Thank you :smile:
Original post by KINGYusuf
Hi, do the intermolecular forces of halogenoalkanes decrease or increase down the group?

Because I swear the boiling points of halogenoalkanes increases down the group due to larger & more halogen atoms. So shouldn't their intermolecular forces increase too?

But a flashcard said that the C-X bonds get weaker as you go down due to shared electrons in a bond getting further from the halogen nucleus


Both points are correct.

Halogens exist as diatomic molecules and have van der Waal's forces between molecules and their neighbouring molecules. When you go down the group, the number of electrons increase and so the number of temporary dipoles and induced dipoles increase. Hence, boiling point and melting points increase as well.

When halogens are bonded to another element (C-X), they are bonded covalently. So yeah, when the distance between the bonding electrons and nuclei increases, the bond strength decreases.

I can't really form a straightforward answer as to why it seems contradictory, but I think it's because it's two different types of forces. van der Waal's is intermolecular and halogens change state when they are broken (i.e melt and boil). Covalent bonds are intramolecular and much stronger and between atoms, not molecules.

And I guess you'd already know this but I figured it was worth mentioning just in case. For halogens in their diatomic state, bond enthalpy decreases from Chlorine. Fluorine has a lower bond enthalpy than Chlorine due to its short bond length causing lone pairs to repel each other.
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Avatar for Dinaa
Dinaa
OP
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Heterogeneous catalysts explained please? :blushing:
[CuCl2]-

charge cl2= -1 and Cu= +1 ??

How?

is it because Cl is -1 then x2 = -2 and +1 because there is a negative charge?
Original post by TheonlyMrsHolmes
[CuCl2]-

charge cl2= -1 and Cu= +1 ??

How?

is it because Cl is -1 then x2 = -2 and +1 because there is a negative charge?



Overall charge = -1

Cu: X

Cl2 = -1

(X) + (2*-1) = -1
(X) + (-2) = -1
X = -1 + 2
X = +1
Original post by thymolphthalein
Overall charge = -1

Cu: X

Cl2 = -1

(X) + (2*-1) = -1
(X) + (-2) = -1
X = -1 + 2
X = +1


I don't understand the -1 answer for 2 *-1? why is that. Sorry I'm so tired my brain has stopped making connections and reached a new stupidity level...:frown:
Original post by Dinaa
Heterogeneous catalysts explained please? :blushing:


Not on the spec. We only need to know specifics about catalytic converters :smile:
Original post by Dinaa
Heterogeneous catalysts explained please? :blushing:


A heterogeneous catalyst is one that is in a different phase (physical state) from the reactants.

Eg: Iron powder catalyst (solid) in Haber process (Nitrogen and Hydrogen gas)

I think only that much is required for AS.

You have to remember three major steps later although I don't recall if it is required to know this in detail for AS.

Heterogeneous. Adsorption. Reaction. Desorption. (H.A.R.D)

Be careful NOT to write absorption.

So for heterogeneous catalysts:

Adsorption: Reactants are adsorbed onto the surface of the catalyst at the active sites, forming some weak bonds.

Reaction: Rate of reaction is increased as adsorption weakens bonds within reactants (weakening activation energy) and changes the orientation of the molecules in such a way that greater proportion of successful collisions occur.

Desorption: Products that are formed are desorbed from the surface and diffuse away from the catalyst
(edited 8 years ago)
Original post by TheonlyMrsHolmes
I don't understand the -1 answer for 2 *-1? why is that. Sorry I'm so tired my brain has stopped making connections and reached a new stupidity level...:frown:


Aha, it's alright. :smile:

20150601_222135.jpg
Original post by itsConnor_
Not on the spec. We only need to know specifics about catalytic converters :smile:


Which exams do you take?

The Edexcel January 2015 IAL paper definitely had a question about heterogeneous catalysts and how they worked for two marks.
Original post by thymolphthalein
Aha, it's alright. :smile:

20150601_222135.jpg


Thank you very much ! :biggrin:
Anyone got any tips what to cover for the AQA AS exam tomorrow?
What parts of the green chemistry do we have to know?
I domt understand how to work out infrared spectroscopy struggling to answer long exam questions on it :frown:
Original post by Kitty201322
I domt understand how to work out infrared spectroscopy struggling to answer long exam questions on it :frown:


Top tip is to label the spectra (which is credited by examiner) and identify functional groups. It may ask you to calculate an impirical / molecular formula first to help you.

For example if there are 2 Os in the molecular formula it can't be a ketone/aldehyde, etc.
Does anyone know how to answer this question:
Antimony is a solid element that is used in industry. The method used for theextraction of antimony depends on the grade of the ore.
3 (a) Antimony can be extracted by reacting scrap iron with low-grade ores that containantimony sulfide (Sb2S3).
3 (a) (i) Write an equation for the reaction of iron with antimony sulfide to form antimony andiron(II) sulfide.

I might be missing something really obvious but I don't get how you're supposed to know how many irons react with the sulfur.
Original post by bob smith 23
Does anyone know how to answer this question:
Antimony is a solid element that is used in industry. The method used for theextraction of antimony depends on the grade of the ore.
3 (a) Antimony can be extracted by reacting scrap iron with low-grade ores that containantimony sulfide (Sb2S3).
3 (a) (i) Write an equation for the reaction of iron with antimony sulfide to form antimony andiron(II) sulfide.

I might be missing something really obvious but I don't get how you're supposed to know how many irons react with the sulfur.

Is this even F322?> :dontknow:
Can someone please explain to me how I do this, and what topic this is. I understand Oxidising alcohols however this question just came up and Im at a lost. Any help is greatly appreciated.

Original post by LordBanter
Can someone please explain to me how I do this, and what topic this is. I understand Oxidising alcohols however this question just came up and Im at a lost. Any help is greatly appreciated.




First things first identify what type of alcohol is it? As the OH is bonded to a C which is bonded to one H (and 2 Cs), it is secondary.

So, for the top left, the acidified potassium dichromate tells you it is oxidised. Secondary alcohols oxidise (heat under reflux) to form ketones - always.
So, I think you take off the OH and replace it with a double bond to O.



Top right: esterification - H comes off the alcohol and OH comes off the carboxylic acid


Bottom left: Dehydration to form alkenes (isomers) - double bond on different carbons for the two boxes.


Check the mark scheme and I hope this helps :smile:

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