Chemistry: Post your doubts here!

[Soldier313]

I don't know why ! But I never seemed to understand chemical energetics with cycles, etc... ! pffffffffff :'(

yup as Amy Bloom said, it just requires practice......inshaAllah you will get the hang of it real soon

 

[NouranAyman]

Anyone taking chemistry AS in november ???

 

[bamteck]

yup as Amy Bloom said, it just requires practice......inshaAllah you will get the hang of it real soon

Ameen

 

[yumichikabyakuya renji]

anyone knows the energy cycle from jn 11 p41 q1)b)
the answer for the lattice energy is -12753 kJ per mol

 

[1357913579]

anyone knows the energy cycle from jn 11 p41 q1)b)
the answer for the lattice energy is -12753 kJ per mol

 

[soumayya]

 

[minhal]

on heating, 0.02 moles of element M reacts with 0.025 moles of Oxygen gas. What is the empirical formula of the oxide of M?
A) M2O
B) MO2
C) MO4
D) M2O5
E) MO5

 

[Student12]

Anyone have notes for planning experiment -A2 ?

 

[autumnsakura]

CAn anyone help me with these 2 questions from june 12?
I don't understand how question 36 includes option 3..

 

[VelaneDeBeaute]

autumnsakura For Q.36 the third option is put adhering to the fact that the reaction is reversible. If you think that the option is not correct, then it is fine. Increase in pressure always shifts the reaction towards the hand-side with fewer moles; in this case the reaction shifts to RHS so the option is wrong! Besides, all three options don't have to be right!
For Q.26. break down the graph into two. The first one then becomes an endothermic reaction curve and the second one becomes an exothermic reaction curve. Now look at the stages and mechanisms of the four reactions individually. Where do you think that first the bonds are broken and then formed? (DIY!)

 

[autumnsakura]

autumnsakura For Q.36 the third option is put adhering to the fact that the reaction is reversible. If you think that the option is not correct, then it is fine. Increase in pressure always shifts the reaction towards the hand-side with fewer moles; in this case the reaction shifts to RHS so the option is wrong! Besides, all three options don't have to be right!
For Q.26. break down the graph into two. The first one then becomes an endothermic reaction curve and the second one becomes an exothermic reaction curve. Now look at the stages and mechanisms of the four reactions individually. Where do you think that first the bonds are broken and then formed? (DIY!)

But for question 36, all three options are the answer. I like your explanation for question 26 though

 

[NouranAyman]

Asalamalaikum guys! Im taking chemistry As in this oct nov session!! its going fine alhamdulilAllah, but I have a feeling Im late in pastpapers cuz im still in begining and Im revizing! Can anyone please help me and give me tips and tell me what level are u guys up to! pleaseeee!!!! thanks

 

[VelaneDeBeaute]

But for question 36, all three options are the answer. I like your explanation for question 26 though

I'm sorry i mis-interpreted the statement. The third option is *The rate of backward reaction increases*! Ofcourse it does. The rate of both the forward and backward reactions increases. Yes, the equillibrium shifts to RHS but because particles are more closer now its easier for them to be converted to products and reactants at the same time. So The more the pressure, the higher the rate.
Just as i made the mistake, i'd like you to remember the difference b/w altering the reaction itself and the rate of reaction. The rate of reaction is independent of the moles etc. and can be increased by increasing temperature or pressure.
Hope this clarifies!

 

[soul]

does anyone know where can I get old chemistry past papers for as/a level (1993-2003) ???
they are not available on xtremepapers.com

 

[MKh@lid]

does anyone know where can I get old chemistry past papers for as/a level (1993-2003) ???
they are not available on xtremepapers.com

May be at a bookshop , they are usually available in a form of a booklet

 

[-rimsa]

on heating, 0.02 moles of element M reacts with 0.025 moles of Oxygen gas. What is the empirical formula of the oxide of M?
A) M2O
B) MO2
C) MO4
D) M2O5
E) MO5

since 0.02 moles of M react with 0.025 moles of Oxygen, 0.02 mole of M reacts with 0.025 x 2 moles of oxygen atoms (oxygen gas is diatomic)
=0.02 mol of M reacts with 0.05 O (atoms)
multiply by 100 to raise the ratio to lowest whole numbers
2:5 =M:O
empirical formula is M2O5 (actual formula could be M2O5, M4O10, M3O15 ... etc.)

 

[Student12]

Anyone have notes for planning experiment -A2 ?

Does anyone have a write up on any of the experiments so i can just get an idea.. HELPP !!!!???

 

[yumichikabyakuya renji]

View attachment 15563

hey thnx this was where i got stuck: why didn't we take 2*+994 kJ/mol for N2??

 

[Amy Bloom]

Does anyone have a write up on any of the experiments so i can just get an idea.. HELPP !!!!???

There are no notes as such, just merge your experiences in the lab and your knowledge of chemistry and practice papers. That's what i would advise you. hope it helped.

 

[soumayya]