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Speciez99
From the AQA specimen paper
8. Write an essay on the chemistry of ammonia.
In your answer you should include a discussion of the bonding in, and the structure of the molecule, considering its industrial preperation and you should bring togeather its reactions in both inorganic and organic chemistry.
(15)
8. Write an essay on the chemistry of ammonia.
In your answer you should include a discussion of the bonding in, and the structure of the molecule, considering its industrial preperation and you should bring togeather its reactions in both inorganic and organic chemistry.
(15)
Got the mark scheme to hand?
I do EdExcel, not sure if the synoptic is anything like yours.. but i'd go for:
* Chemical formula, Dot and cross diagram
* 3D diagram, 107degree bond angle, trigonal pyrimidal
* Covalent bonding within the molecule.. 3BP, 1LP and hence by the Valence Shell Electron Repulsion Theory why the bond angles are 107 and not 109.5
* Intermolecular forces; temporary dipole interactions, permanent dipole-dipole interactions and hydrogen bonding.. maybe also draw the bond dipoles on the 3D diagram to show overall molecular dipole.
* Explanation as to how this causes higher MP / BP and increased solubility than we might expect due to electropositive hydrogen atoms which electrostatically attract the lone pair of electrons on electronegative N of another ammonia molecule. [this is relevant, right?!]
* Industrial preparation via Haber Process, the reaction.. 3H2 (g) + N2 (g) <--> 2NH3 (g) and use of iron catalyst, forward reaction exothermic.
* Sources of raw materials..
The reaction of methane with steam (nickel 700C) to give CO (g) and H2 (g).
The reaction of methane with oxygen and nitrogen (nickel catalyst) to give CO (g), H2 (g) and N2 (g)
Subsequent reaction of carbon monoxide with steam (iron oxide catalyst) to give H2 and CO2 (don't quote me on this).. as the carbon monoxide would otherwise poison the iron catalyst in the chamber.
* Brief explanation of reversible reaction and therefore high pressure / low temperature would drive the position of equilibrium towards NH3. High pressure is firstly a safety concern and the increased cost of building vessel capable of withstanding far higher pressure isn't worth it. Low temperature would give low rate of reaction, hence the use of iron catalyst which increases the rate of both forward and reverse reactions by providing an alternative route by which the reaction can occur, which has a much lower activation energy. Higher proportion of molecules have sufficient energy upon collision to react. 200C and 750 atm would give almost 100% yield, but in industry they use 400C and 200atm which is more realistic. [again, i THINK.. might be small error here?!] So therefore you get relatively high NH3 yield (15%), the catalyst life is relatively long and rate of reaction is at a reasonable level.
* Organics..
Aq Ammonia + Acyl Chloride --> Primary Amine + HCl .. perhaps also an example and structural formulae / functional groups.
Aq Ammoniacal Silver Nitrate.. Tollens reagent used to test for Aldehyde functional group.
Ethanolic Ammonia + Haloalkanes --> Primary Amine + HX (heat under reflux).. and the side reaction of HX + NH3 --> NH4X
[Hmm i'm sure there's a couple more in the organic section!?]
* Inorganics..
Transitiol metals and their deprotonation upon addition of aq. Ammonia.. and then ligand exchange to give an ammine complex;
e.g: [Cu(H2O)6]^2+ + 2NH3 --> Cu(OH)2 + 2NH4^+ + 4H20
then: Cu(OH)2 + 2NH3 + 4H2O --> [Cu(NH3)2(H2O)4]^2+ + 2OH^-
So that gives you a blue ppte, which dissolves to form a deep blue solution, the ammine complex.
[Again, can u think of anything else in inorganics? Purely because i'm too lazy to look it up, NH3 is a STRONG base, right?! No i think it's weak.. Not sure.]
Heh, sorry.. i kinda went for that one a bit more whole-heartedly than i should have, but ne'ermind.
SAHIR.
vp03
im doin nuffield as well and the book is completely useless. does anyone have the markschemes for the end of chapter exam questions? also any good revision sites wud be helpful.
can anyone help me out with working out enthalpy change of combustion?
can anyone help me out with working out enthalpy change of combustion?
Can you be more specific?
The defn. 'Is the enthalpy change the accomopanies the compleat combustion, in air, of 1mole of substance'
LS.
Thanks Ramaya - I'm soooo glad I have someone who knows what they're doing to tell me these things. Do we need to know the energy density calculation as well?
No problem
i don't think the energy density calculation is that major but it might be safer to learn it as it could crop up. Are you redoing the EL and DF module then?Ramaya
No problem i don't think the energy density calculation is that major but it might be safer to learn it as it could crop up. Are you redoing the EL and DF module then?
i don't think the energy density calculation is that major but it might be safer to learn it as it could crop up. Are you redoing the EL and DF module then?Thanks again.
I didn't have any January exams, so all my chem exams (minerals to medicines and chemistry for life) are on the 10th
. Still the revisions going quite well; I've got 6 past-papers/mark schemes (for once, our chem departments got something) to go through. But I feel ready. How's the revision going for you?
LS.
Thanks again.
I didn't have any January exams, so all my chem exams (minerals to medicines and chemistry for life) are on the 10th . Still the revisions going quite well; I've got 6 past-papers/mark schemes (for once, our chem departments got something) to go through. But I feel ready.
How's the revision going for you?
I didn't have any January exams, so all my chem exams (minerals to medicines and chemistry for life) are on the 10th
. Still the revisions going quite well; I've got 6 past-papers/mark schemes (for once, our chem departments got something) to go through. But I feel ready. How's the revision going for you?
Oh no! I didn't realise you didn't do chemistry for life in January! Luckily that exam isn't too bad. Glad to hear the revision is going well! My chemistry department also gave me quite a few past papers (the only subject that did). I've yet to go through them. I havn't done that much chem yet but i've started looking at the bromine extraction process. And theres quite a few salters based websites with quizzes that are getting me through the revision!
Ramaya
Oh no! I didn't realise you didn't do chemistry for life in January! Luckily that exam isn't too bad. Glad to hear the revision is going well! My chemistry department also gave me quite a few past papers (the only subject that did). I've yet to go through them. I havn't done that much chem yet but i've started looking at the bromine extraction process. And theres quite a few salters based websites with quizzes that are getting me through the revision!
Yeah, although in one way, it was a good thing. I was totally unprepared for my bio/psych one just did 'gcse type' revision and got C's.
Wow, I had the exact same thing with exam papers, chem department gave us loads, bio deparment I had to beg to get 2, psychology...well, I didn't expect any, you kinda don't when your teacher only realises you have exams 2wks before and physics we didn't get any.
I'm sure you'll do fine on the papers; you seem very knowledgable about chemistry and the syllabus. You're gonna have lots of fun looking through extraction of bromine/copper - it has got to be one of the most boring parts of the syllabus!
LS.
Yeah, although in one way, it was a good thing. I was totally unprepared for my bio/psych one just did 'gcse type' revision and got C's.
Wow, I had the exact same thing with exam papers, chem department gave us loads, bio deparment I had to beg to get 2, psychology...well, I didn't expect any, you kinda don't when your teacher only realises you have exams 2wks before and physics we didn't get any.
I'm sure you'll do fine on the papers; you seem very knowledgable about chemistry and the syllabus. You're gonna have lots of fun looking through extraction of bromine/copper - it has got to be one of the most boring parts of the syllabus!
Wow, I had the exact same thing with exam papers, chem department gave us loads, bio deparment I had to beg to get 2, psychology...well, I didn't expect any, you kinda don't when your teacher only realises you have exams 2wks before and physics we didn't get any.
I'm sure you'll do fine on the papers; you seem very knowledgable about chemistry and the syllabus. You're gonna have lots of fun looking through extraction of bromine/copper - it has got to be one of the most boring parts of the syllabus!
Woah your physciology teachers are unbelievable! Not realising you have exams lol
. You must've already done your psychology exam (i think). Did that go ok? Lol thanks, you also seem very knowledgable! I like to know the syllabus because i don't like learning unessecery facts, i mean theres enough already.
Yeh bromine and copper extraction (and chlorine too) is oh so joyful
. But i really don't like the reaction mechanism of bromine with ethene. That stuff bores me. And the past papers always have the medicne section intertwined so i wonder why i can't do the question and realise its because we don't have to do that section. Oh well! More next year!Ramaya
Woah your physciology teachers are unbelievable! Not realising you have exams lol . You must've already done your psychology exam (i think). Did that go ok?
Lol thanks, you also seem very knowledgable! I like to know the syllabus because i don't like learning unessecery facts, i mean theres enough already.
Yeh bromine and copper extraction (and chlorine too) is oh so joyful . But i really don't like the reaction mechanism of bromine with ethene. That stuff bores me. And the past papers always have the medicne section intertwined so i wonder why i can't do the question and realise its because we don't have to do that section. Oh well! More next year!
. You must've already done your psychology exam (i think). Did that go ok? Lol thanks, you also seem very knowledgable! I like to know the syllabus because i don't like learning unessecery facts, i mean theres enough already.
Yeh bromine and copper extraction (and chlorine too) is oh so joyful
. But i really don't like the reaction mechanism of bromine with ethene. That stuff bores me. And the past papers always have the medicne section intertwined so i wonder why i can't do the question and realise its because we don't have to do that section. Oh well! More next year!Hee. We're hi-jacking this thread
Yeah, but he was a substitue since our real teacher took six months off. He knew little psychology (he was a sociology teacher). Yup, taken the exams, think it's gone ok.
I wish the CS & CI were devided into the AS and A2 parts - and had clear aims for each chapter - it would make them so much easier to study from. One of the things that really bugs me is reaction conditions - like 'heating under reflux' - since for me, that's just plain remembering rather than understanding.
Right, I'm gonna try and finish this last chem chapter, all the best with the studying
I have various questions to ask regarding Energetics.
1) When calculating the delta H (reaction) given the average bond enthalpies, is it okay to calculate it for the whole equation? I mean if you calculate it for the bonds that are not being broken and not being made, won't these end up just cancelling themselves out?
2) Whats the difference in calculating the:-
i) delta H (formation)
ii) delta H (reaction)
given the delta H (combustion). Won't these two just end up being the same?
And would this just end up being the Sum of delta H (combustion for reactants) - Sum of delta H (combustion for products), taking into account the moles? If this is true, what is the point in setting up a Hess Cycle?
Thanks
1) When calculating the delta H (reaction) given the average bond enthalpies, is it okay to calculate it for the whole equation? I mean if you calculate it for the bonds that are not being broken and not being made, won't these end up just cancelling themselves out?
2) Whats the difference in calculating the:-
i) delta H (formation)
ii) delta H (reaction)
given the delta H (combustion). Won't these two just end up being the same?
And would this just end up being the Sum of delta H (combustion for reactants) - Sum of delta H (combustion for products), taking into account the moles? If this is true, what is the point in setting up a Hess Cycle?
Thanks
hihihihi
first it asked you to write the equation for complete combustion of methanol but then it asks "Suggest why methanol is added to petrol"
only a 1 mark question but i'm guessing it has something to with the equation it asked you to write just before.
any ideas?
only a 1 mark question but i'm guessing it has something to with the equation it asked you to write just before.
any ideas?
Well i methanol contains an Oxygen atom .. so this encourage the Complete Combustion of Fuel producing CO2 instead of CO which is less harmfull.
and also becuz the combustion of methanol is highly exothermic .
Mathemagician
I have various questions to ask regarding Energetics.
1) When calculating the delta H (reaction) given the average bond enthalpies, is it okay to calculate it for the whole equation? I mean if you calculate it for the bonds that are not being broken and not being made, won't these end up just cancelling themselves out?
Not sure as I understand your question. You would calculate whats being broken and whats being made and subject to give the H(reaction) Remember that the values are +Ve for bond breaking and -Ve for making
2) Whats the difference in calculating the:-
i) delta H (formation)
When a substance forms from its elements in their standard states under standard conditions. For example C(s)+O2(g)-->CO2(g)
ii) delta H (reaction)
May not be from elements, for example production of CO2 from buring a hydrocarbon
given the delta H (combustion). Won't these two just end up being the same?
No, see above
And would this just end up being the Sum of delta H (combustion for reactants) - Sum of delta H (combustion for products), taking into account the moles? If this is true, what is the point in setting up a Hess Cycle?
Don't understand the question, sorry
Thanks
1) When calculating the delta H (reaction) given the average bond enthalpies, is it okay to calculate it for the whole equation? I mean if you calculate it for the bonds that are not being broken and not being made, won't these end up just cancelling themselves out?
Not sure as I understand your question. You would calculate whats being broken and whats being made and subject to give the H(reaction) Remember that the values are +Ve for bond breaking and -Ve for making
2) Whats the difference in calculating the:-
i) delta H (formation)
When a substance forms from its elements in their standard states under standard conditions. For example C(s)+O2(g)-->CO2(g)
ii) delta H (reaction)
May not be from elements, for example production of CO2 from buring a hydrocarbon
given the delta H (combustion). Won't these two just end up being the same?
No, see above
And would this just end up being the Sum of delta H (combustion for reactants) - Sum of delta H (combustion for products), taking into account the moles? If this is true, what is the point in setting up a Hess Cycle?
Don't understand the question, sorry
Thanks
you guyz i need help on these questions PLZ
1)What is the maximum yield of each of these products when 58.5Kg of Nacl are electrolysed in brine?
Chlorine,hydrogen,sodium hydroxide ( in Kg )
2) which molecule is planar ?
A.NF3
B.C2Cl4
C.C3H6
D.C3H8
3)Compound X changes the colour of acidified Sodium dichromate(VI) from orange to green. 1 mol of X reacts with 2 mol of HCN(g)
what could X be ?
A.CH3COCH2COCH3
B.CH3CH2CH2CHO
C.H2C=CHCH2CHO
D.OHCCH2CH2CHO
4)The conversation of graphite has only small positive value of enthalpy change
C(graphite) ---> C(diamond) enthalpy change = +2.1Kj mol
however, the production of synthetic diamonds using this reaction is very difficult. [ more than one answer could be right ]
which statment/s help to explain this?
A. The activation energy of the reaction is Large
B. An equilibrium exists between diamond and graphite
C. Only exothermic reactions can be made to occur readily
5)When coal is burnt , gaseous Oxides of carbon and sulphur are formed which pollute the atmosphere. One method of preventing such pollution involves adding calcium carbonate to the burning coal. the temperature of the process cayses the decomposition of calcium carbonate into CaO
[ more than one answer could be right ]
which reactions will be important in helping to reduce atmosphereic pollution??
A. CaO reatcs with SO2 to form calcium sulphite
B. CaO reacts with SO2 abd more Air to form calcium sulphate
C. CaO reacts with CO to form calcium carbonate
And thanks verymuch
1)What is the maximum yield of each of these products when 58.5Kg of Nacl are electrolysed in brine?
Chlorine,hydrogen,sodium hydroxide ( in Kg )
2) which molecule is planar ?
A.NF3
B.C2Cl4
C.C3H6
D.C3H8
3)Compound X changes the colour of acidified Sodium dichromate(VI) from orange to green. 1 mol of X reacts with 2 mol of HCN(g)
what could X be ?
A.CH3COCH2COCH3
B.CH3CH2CH2CHO
C.H2C=CHCH2CHO
D.OHCCH2CH2CHO
4)The conversation of graphite has only small positive value of enthalpy change
C(graphite) ---> C(diamond) enthalpy change = +2.1Kj mol
however, the production of synthetic diamonds using this reaction is very difficult. [ more than one answer could be right ]
which statment/s help to explain this?
A. The activation energy of the reaction is Large
B. An equilibrium exists between diamond and graphite
C. Only exothermic reactions can be made to occur readily
5)When coal is burnt , gaseous Oxides of carbon and sulphur are formed which pollute the atmosphere. One method of preventing such pollution involves adding calcium carbonate to the burning coal. the temperature of the process cayses the decomposition of calcium carbonate into CaO
[ more than one answer could be right ]
which reactions will be important in helping to reduce atmosphereic pollution??
A. CaO reatcs with SO2 to form calcium sulphite
B. CaO reacts with SO2 abd more Air to form calcium sulphate
C. CaO reacts with CO to form calcium carbonate
And thanks verymuch
I know do know how to calculate the delta H (reaction) given either the formation data, combustion data or average bond enthalpy data. What my question is that if you had the delta H (combustion), can you could calculate either the delta H (formation) and the delta H (reaction)?
Also, you know if you are asked to calculate the delta H (reaction) given the formation data the "general formula" is:
Given that you could calculate the delta H (formation) and the delta H (reaction) from the combustion data, would the general formula be: -
?
Sorry, my initial questions werent worded correct.
Also, you know if you are asked to calculate the delta H (reaction) given the formation data the "general formula" is:
Sum of delta H (formation of products) - Sum of delta H (formation of reactants)
Given that you could calculate the delta H (formation) and the delta H (reaction) from the combustion data, would the general formula be: -
Sum of delta H (combustion of reactants) - Sum of delta H (combustion of products)
?
Sorry, my initial questions werent worded correct.
Mathemagician
I know do know how to calculate the delta H (reaction) given either the formation data, combustion data or average bond enthalpy data. What my question is that if you had the delta H (combustion), can you could calculate either the delta H (formation) and the delta H (reaction)?
The dH(reaction) would be the value for dH(combustion), providing that they were the same reaction and that the moles were the same.
The dH(formation) would not be found from the combustion value, but from data books etc.
Also, you know if you are asked to calculate the delta H (reaction) given the formation data the "general formula" is:
Given that you could calculate the delta H (formation) and the delta H (reaction) from the combustion data, would the general formula be: -
Not really, combustion is one specific reaction, it could not be applied to other reactions. Formation and combustion arenot interchangable.
.
The dH(reaction) would be the value for dH(combustion), providing that they were the same reaction and that the moles were the same.
The dH(formation) would not be found from the combustion value, but from data books etc.
Also, you know if you are asked to calculate the delta H (reaction) given the formation data the "general formula" is:
Sum of delta H (formation of products) - Sum of delta H (formation of reactants)
Given that you could calculate the delta H (formation) and the delta H (reaction) from the combustion data, would the general formula be: -
Sum of delta H (combustion of reactants) - Sum of delta H (combustion of products)
Not really, combustion is one specific reaction, it could not be applied to other reactions. Formation and combustion arenot interchangable.
.
FidoDiDo
you guyz i need help on these questions PLZ
1)What is the maximum yield of each of these products when 58.5Kg of Nacl are electrolysed in brine?
Chlorine,hydrogen,sodium hydroxide ( in Kg )
2) which molecule is planar ?
A.NF3
B.C2Cl4
C.C3H6
D.C3H8
.A.
3)Compound X changes the colour of acidified Sodium dichromate(VI) from orange to green. 1 mol of X reacts with 2 mol of HCN(g)
what could X be ?
A.CH3COCH2COCH3
B.CH3CH2CH2CHO
C.H2C=CHCH2CHO
D.OHCCH2CH2CHOThis one. Nucleophilic addition to a carbonyl compound to a substance with an OH group and a CN group where the carbonyl group was. The aldehyde group will give the could change, 2 carbonyl groups so 2 mols HCN
4)The conversation of graphite has only small positive value of enthalpy change
C(graphite) ---> C(diamond) enthalpy change = +2.1Kj mol
however, the production of synthetic diamonds using this reaction is very difficult. [ more than one answer could be right ]
which statment/s help to explain this?
A. The activation energy of the reaction is Large
yes
B. An equilibrium exists between diamond and graphite
not sure. will think about it
C. Only exothermic reactions can be made to occur readily
not this
5)When coal is burnt , gaseous Oxides of carbon and sulphur are formed which pollute the atmosphere. One method of preventing such pollution involves adding calcium carbonate to the burning coal. the temperature of the process cayses the decomposition of calcium carbonate into CaO
[ more than one answer could be right ]
which reactions will be important in helping to reduce atmosphereic pollution??
A. CaO reatcs with SO2 to form calcium sulphite
probably not
B. CaO reacts with SO2 abd more Air to form calcium sulphate
CaO+O+SO2 --> CaSO4
C. CaO reacts with CO to form calcium carbonate
No, it would be CO2
And thanks verymuch
1)What is the maximum yield of each of these products when 58.5Kg of Nacl are electrolysed in brine?
Chlorine,hydrogen,sodium hydroxide ( in Kg )
2) which molecule is planar ?
A.NF3
B.C2Cl4
C.C3H6
D.C3H8
.A.
3)Compound X changes the colour of acidified Sodium dichromate(VI) from orange to green. 1 mol of X reacts with 2 mol of HCN(g)
what could X be ?
A.CH3COCH2COCH3
B.CH3CH2CH2CHO
C.H2C=CHCH2CHO
D.OHCCH2CH2CHOThis one. Nucleophilic addition to a carbonyl compound to a substance with an OH group and a CN group where the carbonyl group was. The aldehyde group will give the could change, 2 carbonyl groups so 2 mols HCN
4)The conversation of graphite has only small positive value of enthalpy change
C(graphite) ---> C(diamond) enthalpy change = +2.1Kj mol
however, the production of synthetic diamonds using this reaction is very difficult. [ more than one answer could be right ]
which statment/s help to explain this?
A. The activation energy of the reaction is Large
yes
B. An equilibrium exists between diamond and graphite
not sure. will think about it
C. Only exothermic reactions can be made to occur readily
not this
5)When coal is burnt , gaseous Oxides of carbon and sulphur are formed which pollute the atmosphere. One method of preventing such pollution involves adding calcium carbonate to the burning coal. the temperature of the process cayses the decomposition of calcium carbonate into CaO
[ more than one answer could be right ]
which reactions will be important in helping to reduce atmosphereic pollution??
A. CaO reatcs with SO2 to form calcium sulphite
probably not
B. CaO reacts with SO2 abd more Air to form calcium sulphate
CaO+O+SO2 --> CaSO4
C. CaO reacts with CO to form calcium carbonate
No, it would be CO2
And thanks verymuch
No rpobs, z!D4N was looking for a challange so might like to check it!!
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