how was chemistry p21?????!!!

[libra94]

@libra94 sorry it was to make C2H2 from the halogenoalkane. I've edited my post. Thanks.

@wonderland I Don't remember my value but I know the answer was = 2 * enthalpy of formation of CO2 + enthalpy of formation of H2O - enthalpy of combustion of C2H2.

It was a +ve value. I think about +27 or something like that.

@exampasser, but that wasnt alkene, that was alkyne!

 

[exampasser]

@libra94 yeah i know but nothing in the syllabus or text book was given for alkyne so I just assumed it was the same.

http://www.organicchemistryreview.com/A ... ebond.html

I've just seen this website as well and it says the same thing.

 

[Saturation]

The enthalpy Formation was: +226kJ mol (It's definitely something 200!)

The gases were SO2, CO2, H20 ( They said only 2 of them are harmful, therefore S02 ----> acid rain and CO2 ---> increase global warming)

The reactions I wrote were:

1) nucleophillic addition
2) elimination
3) hydrolysis (Someone tell me if this is right!!!??)
4) oxidation

And the getting CaSO4 from Ca(NO3)2, it said WITHOUT an acid----> the reagent is potassium sulfate (I think there can be others too!)

 

[libra94]

The enthalpy Formation was: +226kJ mol (It's definitely something 200!)

The gases were SO2, CO2, H20 ( They said only 2 of them are harmful, therefore S02 ----> acid rain and CO2 ---> increase global warming)

The reactions I wrote were:

1) nucleophillic addition
2) elimination
3) hydrolysis (Someone tell me if this is right!!!??)
4) oxidation

And the getting CaSO4 from Ca(NO3)2, it said WITHOUT an acid----> the reagent is potassium sulfate (I think there can be others too!)

i wrote reduction

 

[mmarei94]

So guys what do you think the answer for the "suggest why ethanethiol is added to butane"? I wrote to alert people of gas leakages...does anyone know if this is right? because the question clearly said that the compound was one of the worst-smelling compounds in the world.
And the enthalpy of formation was +226 Kjmol-1
Wish you all the best inshallah

 

[exampasser]

@Saturation, SO4 ions are more reactive than NO3 ions so i think the reagent has to be of a metal thats less reactive than Ca eg MgSO4 or ZnSO4 etc any metal sulfate with a metal which is less reactive than Ca.

And i wrote the same reactions you got

@mmarei94, i had no idea what to write for that question your point makes sense though! Because the question said the gas was liquified i wrote so that people dont drink the liquid. Because the compound smelt so bad people people wouldnt drink it but its probably wrong.

 

[wonderland]

what was the answer for last question the one with 6 marks i got +60 kjmol-1 .however few of my of friend got something +225 what was the answer.
the way i did was as is to find the enthapy of formation.........
2H2 + 2C --> C2H4
Product - reactants
s0 (-1300)-(2(-288) + 2(392)) = +60kjmol-1

IT CANT BE +200 SOMETHING BECAUSE IT WAS C2H4(ETHENE) NOT C2H2(ALKYNE) S0.........YOU GET WHAT QUOTED....
RATHER COMPLICATED EXPLANATION GIVEN TO ME BY YOU ME REALLY IRRITATES ME....
I KNOW YOU GET +266 SOMETHING IF
H2 + 2C --> C2H2
S0 2(-288) + 2(392))-(-1300)=+266 KJMOL-1-------------SO IT IS WRONG
BY THE WAY IT WAS 4 MARKS 2MARKS FOR ERQUATION MAKING COMBUSTION AND FORMATION ONE.........

IF I AM TO BE WRONG PLEASE CORRECT ME ASAP :shock: :O:

 

[filza94]

gr8 this has to be locked

 

[Saturation]

@Saturation, SO4 ions are more reactive than NO3 ions so i think the reagent has to be of a metal thats less reactive than Ca eg MgSO4 or ZnSO4 etc any metal sulfate with a metal which is less reactive than Ca.

I just guessed that one, and I checked on the net, apparently calcium nitrate plus potassium sulfate = pottasium nitrate plus calcium sulfate! :Search:

And yeah, the ethanoide thing in the gas is to alert people if the gas leaks! lol drinking butane!

 

[Saturation]

And yeah, the enthalpy change is definitely 226! Check wikipedia!:

Ethyne Gas C2H2 226.73

http://en.wikipedia.org/wiki/Standard_e ... a_table%29

 

[exampasser]

@Wonderland I think it was enthalpy change of formation of C2H2 because my equation for the enthalpy change of combustion was :

C2H2 + 2.5O2 ---> 2CO2 + H2O

So enthalpy change of formation = 2(enthalpy change of formation of CO2) + (enthalpy change of formation of H2O) - (enthalpy change of combustion of C2H2)

Using your values the answer = 2(-392) + (-228) - (-1300) = +288 kJ mol-1

 

[wonderland]

this is wrong i am sure

 

[wonderland]

enthalpy of formation is formation of compound from its element........ it C2H4

http://ocw.mit.edu/courses/chemistry/5- ... 16_s05.pdf

OXIDITION OF ALKYNES WONT GIVE CO2 + H20

 

[exampasser]

Saturation i looked it up on the net and it seems both of our answers would give calcium sulfate lol

 

[exampasser]

Wonderland it wasn't C2H4 it was C2H2!

 

[Saturation]

Saturation i looked it up on the net and it seems both of our answers would give calcium sulfate lol

:Yahoo!: :Yahoo!: :Yahoo!: :Yahoo!: :Yahoo!:

 

[wonderland]

enthalpy of formation is formation of compound from its element........ it C2H4(ETHYLENE) NOT C2H2(Acetylene (systematic name: ethyne)

http://ocw.mit.edu/courses/chemistry/5- ... 16_s05.pdf

OXIDITION OF ALKYNES WONT GIVE CO2 + H20

exampasser CHECK THIS

 

[exampasser]

Wonderland that's oxidation not combustion. There's a difference isn't there?

Eg. Alcohols can be oxidised to aldehydes or ketones but they are combusted to carbon dioxide and water.

 

[wonderland]

OK BUT R U SURE THAT IT C2H2(Acetylene (systematic name: ethyne) NOT C2H4(ETHYLENE)

 

[exampasser]

Yes quite sure.