OCR AS - Chemistry Unit F322 - Chains, energy and resource - REVISION!

Reply 460

786girl

someone answer my previous post plzz!!

Reply 461

touran22

Original post by hash007

Can someone quickly run through Greenhouse gas effect :colondollar:

How to answer it if it was a 6 marker!

green house gases (CO2. CH4 CFC) absorb radiation from the sun. this causes there bonds to vibrate at different frequencies. The stronger the bond vibrates the more potent the greenhouse gas is. they molecules then re emit this radiation towards the surface of the earth. an increase in these gases means more radiation is re emited to the earth which disturbs the steady state system and thus causes global warming.

Reply 462

Killjoy-

8

Original post by 786girl

1. if u hve nucleophilic substituition and use NH3 would you draw NH2- with a lone pair?

2.can someobe give me an easy full scoring definition of BOND ENTHALPY and AVG. BOND ENTHALPY.

3.xplain the importance of controlling global warming caused by atmospheric increase in greenhouse gases (???)

4. outline role played by chemists ???

5. PRINCIPLES?!?!?!

boooorrriiiinggggggggggggg

lol

I have to do some revision, but I'll answer the first. The nitrogen in NH3 has a lone pair on it (that's how NH4+ can form as a H+ forms a dative covalent bond with it)

From textbook: Bond enthalpy- the enthalpy change that occurs when breaking by homolytic fission one mole of a given bond in the molecules in the molecules of a gaseous species. For average you add 'given type of bond' instead of given bond.

In papers I've seen different definitions though.

Reply 463

hash007

15

Original post by touran22

green house gases (CO2. CH4 CFC) absorb radiation from the sun. this causes there bonds to vibrate at different frequencies. The stronger the bond vibrates the more potent the greenhouse gas is. they molecules then re emit this radiation towards the surface of the earth. an increase in these gases means more radiation is re emited to the earth which disturbs the steady state system and thus causes global warming.

Hmm mark scheme says you have to talk about UV radiation going to earth first, then re emitted from earth as Infared radiation, then talking about the bond vibrations :colonhash:

Reply 464

touran22

Original post by timkench

pretty sure H-Cl has dipols due to large difference in electronegativities, and hetrolytic fission takes place, check the textbook

hmm...well i was just thinking HBR reacts with alkenes in electrophilic addition reactions so if this was HCL and an alkene it would be addition.

However if it was a halogeno alkane reacting with OH- then it was substution .

Reply 465

touran22

Original post by hash007

Hmm mark scheme says you have to talk about UV radiation going to earth first, then re emitted from earth as Infared radiation, then talking about the bond vibrations :colonhash:

which book do you have? see this was the definition givin in the Biology syllabus but in this chemistry that was what the book had on global warming. :confused:

Reply 466

timkench

2

Original post by 786girl

1. if u hve nucleophilic substituition and use NH3 would you draw NH2- with a lone pair?

2.can someobe give me an easy full scoring definition of BOND ENTHALPY and AVG. BOND ENTHALPY.

3.xplain the importance of controlling global warming caused by atmospheric increase in greenhouse gases (???)

4. outline role played by chemists ???

5. PRINCIPLES?!?!?!

boooorrriiiinggggggggggggg

lol

1. nh3 with one

2. enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species

3.rising sea levels etc? CFCs have a very long life span, need to control now

(edited 12 years ago)

Reply 467

timkench

2

Original post by touran22

hmm...well i was just thinking HBR reacts with alkenes in electrophilic addition reactions so if this was HCL and an alkene it would be addition.

However if it was a halogeno alkane reacting with OH- then it was substution .

yeah thats what i thought :smile:

Reply 468

lolo-x

Original post by 786girl

1. if u hve nucleophilic substituition and use NH3 would you draw NH2- with a lone pair?

this was in the January 2011 paper. you draw NH3 with a lone pair :smile:

not NH2-

Original post by 786girl

2.can someobe give me an easy full scoring definition of BOND ENTHALPY and AVG. BOND ENTHALPY.

bond enthalpy: the enthalpy change when one mole of a given bond is broken in the gaseous state

average bond enthalpy: the average enthalpy change that takes please when one mole of a given bond is broken in the molecules of a gaseous species

Original post by 786girl

3.xplain the importance of controlling global warming caused by atmospheric increase in greenhouse gases (???)

thats a bad question, what do you mean? :/
- each type of bond absorbs infrared of a particular frequency
- causing the bonds to vibrate more
- this energy is transferred to other molecules by collisions
- increasing their kinetic energy
- so increasing temperature?

Original post by 786girl

4. outline role played by chemists ???

- provide scientific evidence to governments to verify that global warming exists
- investigate solutions to environmental problems e.g. CCS
- monitor progress against initiatives such as the kyoto protocol

Original post by 786girl

5. PRINCIPLES?!?!?!

- reduce the use of hazardous chemicals
- reduce the amount of waste
- recycle the waste
- use fewer chemicals
- design for energy efficiency
- use renewable feedstocks
- manufacture biodegradable products
- think safety
- establish international cooperation

(edited 12 years ago)

Reply 469

Obadetona

14

Original post by hash007

I thought it was electrophillic substitution as the OH was being substituted for a Cl, but mark scheme says Nucleophillic substitution.

GUYS

In Salters AS there's no such thing as nucleophilic addition or electrophilic addition

ONLY:
Nucleophilic substitution
Electrophilic addition

Addition is when 2 reactants form one product

Substitution is when a part of the molecule is substituted/replaced

Reply 470

hash007

15

Original post by touran22

which book do you have? see this was the definition givin in the Biology syllabus but in this chemistry that was what the book had on global warming. :confused:

I got this from the past paper mark sheme, but it says the same thing in the book. I use the OCR Chem Salters Revision book. Think i'm just gonna make notes on it all night, then do a few past papers in the morning, left it too late again :l
But on a positive note I got an A in my mock, so hopefully I won't do worse :tongue:

it's just the advanced notice article thats gonna be tricky.

Reply 471

ChessMister

12

what time is this exam??!!

Reply 472

High VOLTAGE

11

Original post by flint_09

i figured out, in fact it is the opposite of what u said.

(2.5 x 10^5)/4 x 909

Original post by jim lee

i know in all the papers i have done, they say ignore all dots for the ocr a papers. So if you put them in, they might change their marking criteria, but if they dont, they wont look at it. I put them in anyway, just in case they change it for tomorrow.

I must be one of the few people that love the long questions at the end of the paper. I like the questions when they ask you to draw the boltsmann distribution and enthalpy profile diagram for a catalysed reaction-easy 7-8 marks there for me. I think the identifying compounds questions at the end, like when they give you data like mass spectrometry, infrared spectroscopy etc, are pretty good as well. But that is probably just me....

Original post by lolo-x

if anyone wants to see some notes, i've attached mine here and pleeease let me know if there's anything wrong or missing that i need to know about! :smile:

if 2.5x10^5 mol of no produced each day if h=-909, how much energy released each day there are 4mol of no?
The answer is / 5.7 × 10^7
helllp please

Reply 473

hash007

15

Original post by lolo-x

x

Hi, could I see your notes please don't know where you posted them :colondollar:

yet to make my own yet

Reply 474

lolo-x

Original post by touran22

hmm...well i was just thinking HBR reacts with alkenes in electrophilic addition reactions so if this was HCL and an alkene it would be addition.

However if it was a halogeno alkane reacting with OH- then it was substution .

its definitely electrophilic addition because for it to be nucleophilic substitution you would need a nucleophile (electron pair donor: e.g. OH-, H2O, NH3, CN-)

Reply 475

786girl

Original post by hash007

I got this from the past paper mark sheme, but it says the same thing in the book. I use the OCR Chem Salters Revision book. Think i'm just gonna make notes on it all night, then do a few past papers in the morning, left it too late again :l
But on a positive note I got an A in my mock, so hopefully I won't do worse :tongue:

it's just the advanced notice article thats gonna be tricky.