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OCR Chemistry F322~ 4th June 2013~ AS Chemistry

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oka I have a question for you guys! it comes up a lot....................................why are catalyst used in industrial process...4 marks

Reply 2201

Blashnet

Original post by Sam_1996

-recycle them
-burn them for fuel
-landfill sites
But i can't get a fourth

feedstock/cracking

Reply 2202

simifeltham

Original post by Sam_1996

-recycle them
-burn them for fuel
-landfill sites
But i can't get a fourth

Cracking,Biodegradable and photodragradable polymers

Reply 2203

Hello...

Original post by simifeltham

State four ways in which polymers are disposed?

Burned to produce energy
Sorted and Recycled
Feedstock recycling
Cracking to form new polymers??

Reply 2204

Blashnet

Original post by geekD96

oka I have a question for you guys! it comes up a lot....................................why are catalyst used in industrial process...4 marks

Speed up reactions
lower activation energy
less fossil fuels/less co2
alternate routes can be discovered
less toxic gas

Reply 2205

Freyaa

Original post by Blashnet

omg thankyou!! :biggrin:

So any radical has undergone homolytic fission?

Yes because a radical has an unpaired electron :biggrin:

Reply 2206

JimmyA*

Original post by reneetaylor

Okay, thanks Jimmy.
I was thinking that as the c=c bond is going to involve the first carbon anyway.

I panicked as I thought you had to be precise!

If it's got more than 3 carbons it's safe to start calling compounds but-1-ene or pent-2-ene I think :smile:

Yes, if its got more than 3 carbons then you have to.

Reply 2207

anonymousecheese

Can someone please explain whats going on/help me?
i was marking my june 2010 question: 1e
the answers i got were 1.56x10^-3 for part 2 and 1.5x10^-6 for part 3
but the mark scheme answers are different :confused:

1.56x10^4 and 1.5x10^4 repectively
i am so confused, is something wrong with my calulator?

Reply 2208

Kits

Afternoon exams are so poor

Reply 2209

Nas.

Which definitions are likely to come up, apart from enthalpy of combustion/formation/reaction?

Reply 2210

simifeltham

Original post by geekD96

oka I have a question for you guys! it comes up a lot....................................why are catalyst used in industrial process...4 marks

The provide an alternative reaction pathway with lower Ea so the reaction can occur at a lower temperature. They are not used up in the reaction and they increase atom economy. Produce less CO2. Increase the rate of reaction so there are more successful collisions between particles.

Reply 2211

geekD96

did your teachers give you any hints?????/

Reply 2212

Blashnet

Original post by simifeltham

Heterolytic the covalent bond brakes and both electrons go to one atom
Homolytic the covalent bond brakes and one electron goes to each carbon forming radicals.

e.g Heterolytic - HBr -> H+ + Br-

Homolytic Cl2 -> Cl. + Cl.

does that mean, in nucleophilic substitution, it's always heterolytic?

Reply 2213

Freyaa

Original post by anonymousecheese

1.56x10^4 and 1.5x10^4 repectively
i am so confused, is something wrong with my calulator?

I got the same I don't understand how to get the answer on the markscheme:/

Reply 2214

simifeltham

Original post by Blashnet

does that mean, in nucleophilic substitution, it's always heterolytic?

It is indeed but so are electrophilic addition reactions.

you will only really come across homolytic fission in ozone depletion reactions or radical substitutions

(edited 10 years ago)

Reply 2215

geekD96

Original post by Kits

Afternoon exams are so poor

aww you will be fine think positive ... to be honest I prefer afternoon ones...after lunch lol in the mornings I feel tired and hungry and sick :frown:

Reply 2216

reneetaylor

Original post by Blashnet

does that mean, in nucleophilic substitution, it's always heterolytic?

Both of the bonded electrons will go to one of the bonded atoms, forming an ion- in heterolytic fission that is.

So heterolytic it's usually involved in a bond where there are atoms of different species

For example in H-Br, bromine is the most electronegative and therefore takes both of the bonded electrons in the covalent bond, making it more negative.

You will notice that heterolytic fission occurs mostly in nucelophilic substitution, where a dipole is induced in a C-X (X= halogen) bond, halogen takes both of the bonded pair of electrons, leaving a carbocation which is positively charged.

The nucleophile can be anything from OH to...anything else (lol), and this will form a bond with the carbocation, leaving the halogen.

Reply 2217

geekD96

Original post by simifeltham

It is indeed

nucleophillic=heterophilic...and electrophilic=homo? is this right

Reply 2218

anonymousecheese

Original post by Freyaa

I got the same I don't understand how to get the answer on the markscheme:/

ok so its not my calculator...its me :confused:

Reply 2219

Hello...

Original post by JimmyA*

Here's a few good questions:
Why does the pi-bond break and not the sigma bond?(it's a question which alot of people forget and hasn't come up for a while)
What is the advantage of using the ziegler-natta process over radical polymerisation?
What are the current problems with storing Carbon in stable minerals?

I'd say that the pi bond is weaker than the sigma bond so less energy is required to break it...
Radical polymerisation forms too many products ( at a guess, never heard of zeigler-natta)
Not sure about last one :confused:

[EDIT] When reactin CO2 with metal oxide the reaction rate is very slow and a lot of energy is needed to speed up the reaction making it an unreasonable solution