• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Chemistry: Post your doubts here!

Messages
4,062
Reaction score
25,658
Points
523
wa alaykum salaam
Firstly, I'm so mad I concentrated so much on this and then realised it was A2 afterwards...:D
I haven't done A2 so I may be wrong but it seems like compound D has to be a carbonyl compound, and the functional group you've given is not a carbonyl compound.
Hahahaha :p Atleast u tried :)
Umm its actually some reaction of iodomethane in A2 part

Ok y are u saying it shud be carbonyl compound?
 
Messages
17
Reaction score
1
Points
3
Can anyone explain this to me? Thank You.!

E. Change of formation of CO2= -395kjmol^-1
E. Change of formation of H2O= -297kimol^-1
E. Change of combustion of C2H6= -1620kJmol^-1

Calculate the enthalpy of the formation of ethane.
[-2(395)+3(-297)]-(-1620)
= -61kJmol^-1

WHY?
 
Last edited:
Messages
2,515
Reaction score
4,065
Points
273
Can anyone explain this to me? Thank You.!

E. Change of formation of CO2= -395kjmol^-1
E. Change of formation of H2O= -297kimol^-1
E. Change of combustion of C2H6= -1620kJmol^-1

Calculate the enthalpy of the formation of ethane.
[-2(395)+3(-297)]-(-1620)
= -61kJmol^-1

WHY?
Use Hess's Law and construct a cycle

2C + 3H2 ---> 2CO2 + 3H20 (These are the Del H of formation of CO2 and H20)
C2H6 + 3.5O2 ----> 2CO2 + 3H20 ( Del H of Comb of ethane)

As you can see both have the same products,hence you can construct a cycle and work out how C2H6 can be formed from 2C and 3H2.The cycle would give

2(-395) + 3(-297) = Del H of formation + (-1620)

Solve it and you'll get -61 kJ/mol

Read this too:http://www.chemguide.co.uk/physical/energetics/sums.html
 
Messages
603
Reaction score
1,102
Points
153
Can anyone explain this to me? Thank You.!

E. Change of formation of CO2= -395kjmol^-1
E. Change of formation of H2O= -297kimol^-1
E. Change of combustion of C2H6= -1620kJmol^-1

Calculate the enthalpy of the formation of ethane.
[-2(395)+3(-297)]-(-1620)
= -61kJmol^-1

WHY?

Construct an equation for combustion of ethane.

C2H6 + 3.5O2 ----> 2CO2 + 3H20

Heat of combustion (reaction) = heat of formation of products - heat of formation of reactants
 
Messages
155
Reaction score
27
Points
28
HNE is a reactive compound.
CH3(CH2) 4CH(OH)CH=CHCHO
(c) Give the structural formulae of all of the carbon-containing compounds formed in each case when HNE is reacted separately with the following reagents.

(i) hot concentrated manganate(VII) ions in acid solution.

So what I came up with is: CH3(CH2)4CH(OH)CO2H + HO2CHO

but in the markscheme the OH- group and the CHO group have also been oxidised giving: CH3(CH2)4COCO2H and HO2CCO2H

What i don't get is that it says manganate ions, not dichromate, so how can the alcohol and the aldehyde group get oxidised as well?
 
Messages
1,229
Reaction score
740
Points
123
Q what will be the result of oxidising this compound with Hot conc K2cR2O7.
Acc to me there should be no change!! any help will be appreciated!
 

Attachments

  • image.jpg
    image.jpg
    92.5 KB · Views: 16
Messages
2,515
Reaction score
4,065
Points
273
HNE is a reactive compound.
CH3(CH2) 4CH(OH)CH=CHCHO
(c) Give the structural formulae of all of the carbon-containing compounds formed in each case when HNE is reacted separately with the following reagents.

(i) hot concentrated manganate(VII) ions in acid solution.

So what I came up with is: CH3(CH2)4CH(OH)CO2H + HO2CHO

but in the markscheme the OH- group and the CHO group have also been oxidised giving: CH3(CH2)4COCO2H and HO2CCO2H

What i don't get is that it says manganate ions, not dichromate, so how can the alcohol and the aldehyde group get oxidised as well?
Well,isnt KMnO4 an oxidising agent?IT IS first and foremost,its the conditions that cause it to break the C=C,but along with that it will oxidise anything it can ,which include the OH and COH groups.

It isnt just for breaking the C=C,it oxidises too and that you shouldnt forget.Both k2cr207 and kmn04 oxidise equally,its that the conditions of kmn04 give some unique qualities to it,but if it oxidises in hot and conc form,it'll be most effective and oxidise all fully,as well as break the bond.
 
Messages
1,229
Reaction score
740
Points
123
Yeah, its not a CIE question..
I am just confused that is it correct to say that k2cr2O7 doesn't react with alkene under any conditions whatsoever? or can it react under hot conc conditions?
 
Top