Chemistry: Post your doubts here!

[ashcull14]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_42.pdf
question 5 c(iv). Why can't we add a side chains ? Doesn't this increase van der waals force and so it becomes more rigid ?

side chains decrease the contact between the molecules so vender waals forces become weaker and the material becomes weaker ..less dense and softer

 

[Bhaijan]

year 04 june p1
i cant get this

Ans is 1
why cant 3 be correct

 

[qwertypoiu]

year 04 june p1
i cant get this

Ans is 1
why cant 3 be correct


View attachment 59960

Well some endothermic reactions can occur readily. For example, salt dissolving is an endothermic process (sometimes) and it happens readily.
Thermal decomposition of CaCO3 at high temperatures "occurs readily".
Spontaneity of a reaction doesn't only depend on enthalpy change of it. Something known as entropy has to be taken into account as well. You'll learn more about entropy in A2

 

[Eugene99]

year 04 june p1
i cant get this

Ans is 1
why cant 3 be correct


View attachment 59960

Even endothermic reacctions occur spontaneously. Actually, the spontaneity of reaction is determined by 2 factors: changes in enthalpy, Δ H and entropy. Though, mostly it's the Δ H that determines the spontaneity but even entropy matters, so since 3 says 'Only exothermic reactions can be made to occur readily', the use of word only makes it wrong, as endothermic can also be spontaneous

 

[Eugene99]

Well some endothermic reactions can occur readily. For example, salt dissolving is an endothermic process (sometimes) and it happens readily.
Thermal decomposition of CaCO3 at high temperatures "occurs readily".
Spontaneity of a reaction doesn't only depend on enthalpy change of it. Something known as entropy has to be taken into account as well. You'll learn more about entropy in A2

seems like we two wrote the same thing at the same time xD

 

[qwertypoiu]

seems like we two wrote the same thing at the same time xD

Haha yeah

 

[Saad the Paki]

The Ans is A(all statements are correct). I get how statement 2 is correct but what about statement 1 and 3? How are they correct?:/

 

[Saad the Paki]

Ans is B, how?

 

[qwertypoiu]

View attachment 59963 The Ans is A(all statements are correct). I get how statement 2 is correct but what about statement 1 and 3? How are they correct?:/

When graphite is converted to diamond, energy is put IN to the system. It means diamond's bonds are weaker and longer than those of graphite. When you atomize both of them, you want to continue this process of weakening the bonds so they are completely separated. Since diamond already has slightly weaker bonds, lesser energy has to be put into it to achieve this.

When you combust, you put energy into these species (the activation energy) and then ALL of it comes back out to the surrounding, and even more is released. (Exothermic reaction)
Therefore, since diamond has a little more energy put into it, it will release more energy. Or another way to think of it, less activation energy will be used on diamond, so the overall energy released will be greater.

In diagrams below, energy diagrams are shown. Diamond is in red. It shows the difference in energy changes in an endothermic reaction (atomization) and an exothermic reaction (combustion).

 

[Shah34]

Aoa Guys
Plz help with this question ASAP
Thanks Q25

 

[qwertypoiu]

Aoa Guys
Plz help with this question ASAP
Thanks Q25
View attachment 59972

Should be 8.
There are 3 double bonds. Each can either be cis or trans.
So 2^3 = 8

 

[qwertypoiu]

Ans is B, how? View attachment 59964

Inititially, each of the three side chains has 3 double bonds.
One is converted such that 2 double bonds are left. (i.e. One of it has undergone addition)
The other two are converted such that only 1 double bond is left. (i.e. Two double bonds have been removed)
So in total, the number of double bonds removed is 2x2+1 = 5.
Each double bond requires one mole of H2 to be hydrogenated, so your answer is 5.

 

[Shah34]

Should be 8.
There are 3 double bonds. Each can either be cis or trans.
So 2^3 = 8

Yess
I had forgotten about that,
Thanks

 

[Anika97]

can anyone help me with question 5(a) of O/N/09/42
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_42.pdf

 

[qwertypoiu]

can anyone help me with question 5(a) of O/N/09/42
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_42.pdf

I previously answered this here. See if it helps.

 

[Anika97]

I previously answered this here. See if it helps.

Thank you so much!!!!!

 

[Shah34]

Can someone please post proper AS practical notes covering all main topics
Please!!!

 

[holoholo]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_51.pdf

How can you prepare the different concentrations ?

 

[qwertypoiu]

View attachment 59985

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_51.pdf

How can you prepare the different concentrations ?

Remember that last time you asked something very similar?
It's the same steps I'm afraid

 

[qwertypoiu]

Can someone please post proper AS practical notes covering all main topics
Please!!!

A Level Chemistry Paper 3 Notes
The above was created by Rizwan Javed so credit goes to him