Physics, Chemistry and Biology: Post your doubts here!

[Phoenix Blood]

Subject : Chemistry

Can somebody explain the Lechatlier's principle and what happens during an exothermic and an endothermic reaction.

Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings.

Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.

 

[Atharva Joshi]

Can anybody suggest a really good chemistry coursebook?

 

[My Name]

Predict the products of the electrolysis of a specified
binary compound in the molten state
wta is that suppose to mean?

 

[My Name]

Describe electrolysis in terms of the ions
present and reactions at the electrodes in
the examples given?

 

[Phoenix Blood]

Predict the products of the electrolysis of a specified
binary compound in the molten state
wta is that suppose to mean?

Meaning if you electrolyse a binary compound (A binary compound is a chemical compound that contains exactly two different elements. Eg, NaCl, CaS04, etc) , what products will you get, if the reactants are in the molten state and have no water in it, at the cathode and the anode (?)
For this, you'll need to learn the preferential discharge of anions and cations.

 

[Phoenix Blood]

Describe electrolysis in terms of the ions
present and reactions at the electrodes in
the examples given?

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electrolysis/electrolysisrev1.shtml

 

[My Name]

Meaning if you electrolyse a binary compound (A binary compound is a chemical compound that contains exactly two different elements. Eg, NaCl, CaS04, etc) , what products will you get, if the reactants are in the molten state and have no water in it, at the cathode and the anode (?)
For this, you'll need to learn the preferential discharge of anions and cations.

so u mean i shud know wat cums at cathoda and anode

 

[Phoenix Blood]

so u mean i shud know wat cums at cathoda and anode

Yes, when the binary compound is in the molten state.
If it is dilute, it contains water, and then the results will differ because oxygen or hydrogen also maybe discharged at the electrodes then (H20)

 

[My Name]

For this, you'll need to learn the preferential discharge of anions and cations.
means lik ethat umm that hydrogen opr metal at cathopde and aat anode a gas like chlorine bromine

 

[My Name]

Yes, when the binary compound is in the molten state.
If it is dilute, it contains water, and then the results will differ because oxygen or hydrogen also maybe discharged at the electrodes then (H20)

we dont need to use Binary word do we?

 

[Phoenix Blood]

we dont need to use Binary word do we?

I guess, no. Lol.

 

[My Name]

th

I guess, no. Lol.

nx

 

[Phoenix Blood]

For this, you'll need to learn the preferential discharge of anions and cations.
means lik ethat umm that hydrogen opr metal at cathopde and aat anode a gas like chlorine bromine

Yes. And better.

 

[Mr.Physics]

Describe electrolysis in terms of the ions
present and reactions at the electrodes in
the examples given?

Hey the question requires you to give ions present in the reaction and what happened at different electrodes when a reaction occured .
So first you should learn the reactivity series of ions. It means that if there is a reaction containing H+and Na+ , then which cation will go towards cathode ?? It will be H+ because it takes less energy to get discharged. However , if the concentration of Na +will be higher, then it will be discharged. The list of reactivity series should be there in your book.

And in the case of electrodes , you have to learn what happenes at different electordds in different reactions.

 

[My Name]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s06_qp_1.pdf
questions
16
19
21
39
40

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_qp_1.pdf
question 7

 

[My Name]

@Phoenix Blood
fenix can u help ?

 

[Phoenix Blood]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s06_qp_1.pdf
questions
16
19
21
39
40

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_qp_1.pdf
question 7

*Remember most oxides, hydroxides, carbonates and hydrogen-carbonates are either alkalis or bases with a Ph above 7

16) D.
What happens to the pH of a solution of hydrochloric acid as an excess of aqueous barium
hydroxide is added?
HCl is acidic, and barium hydroxide is basic. If excess BaOH is added to HCl, we come to understand that more of the base (BaOH) remains after complete neutralization of the HCl. So the solution goes from Ph 1 (HCl) to beyond neutralization, i.e. Ph 14. Neutralization is Ph 7 as we know.

19) C.
Cu + H2SO4 --> Copper does not react with dilute sulphuric acid.
Cu(OH)2 + H2SO4 --> CuSO4 + H2O (not balanced) .....here we have CU2+ ions
CuCO3 + H2SO4 ---> CuSO4 + CO2 + H2O .....here we have CU2+ ions

21) A.
Ionic compounds are formed b/w a metal and a non-metal.
Covalent compounds are formed bw two non-metals.
(Starting 3 groups are metals, last group contains unreactive elements. The remaining elements are non-metals and metalloids. )
W and X are non-metals so they'll form a covalent compound, Y is a metal, and Z unreactive.

39) C
A has double and single bonds.
B has double and single and triple bonds b/w Carbon atoms
C has all double bonds b/w Carbon atoms, and hence all belong to the same homologous series.
D also has varying single and double bonds b/w varying elements.

40) B
When an alkene (Double bonds b/w two carbon atoms) links with another alkene, the double bond breaks in both to join with the other alkene, and all the rest of the atoms stay same and undisturbed.

 

[Phoenix Blood]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_qp_1.pdf
question 7

Covalent compunds are formed b/w a non-metal and another non-metal.
Since the electrons in the outer shell correspond to the group number, we know that elements with a valency of 1 and 2 are metals. A valency of 6 and 7 means they are both non-metals and hence will react to form a covalent compound.

Another way we can use to find out the answer is to know that non-metals for acidic oxides and hences will be in the later groups with valencies of 6, 7 and 8. One element we can know that is being used here is oxygen which will too be in the latter groups.

 

[My Name]

Covalent compunds are formed b/w a non-metal and another non-metal.
Since the electrons in the outer shell correspond to the group number, we know that elements with a valency of 1 and 2 are metals. A valency of 6 and 7 means they are both non-metals and hence will react to form a covalent compound.

Another way we can use to find out the answer is to know that non-metals for acidic oxides and hences will be in the later groups with valencies of 6, 7 and 8. One element we can know that is being used here is oxygen which will too be in the latter groups.

*Remember most oxides, hydroxides, carbonates and hydrogen-carbonates are either alkalis or bases with a Ph above 7

16) D.
What happens to the pH of a solution of hydrochloric acid as an excess of aqueous barium
hydroxide is added?
HCl is acidic, and barium hydroxide is basic. If excess BaOH is added to HCl, we come to understand that more of the base (BaOH) remains after complete neutralization of the HCl. So the solution goes from Ph 1 (HCl) to beyond neutralization, i.e. Ph 14. Neutralization is Ph 7 as we know.

19) C.
Cu + H2SO4 --> Copper does not react with dilute sulphuric acid.
Cu(OH)2 + H2SO4 --> CuSO4 + H2O (not balanced) .....here we have CU2+ ions
CuCO3 + H2SO4 ---> CuSO4 + CO2 + H2O .....here we have CU2+ ions

21) A.
Ionic compounds are formed b/w a metal and a non-metal.
Covalent compounds are formed bw two non-metals.
(Starting 3 groups are metals, last group contains unreactive elements. The remaining elements are non-metals and metalloids. )
W and X are non-metals so they'll form a covalent compound, Y is a metal, and Z unreactive.

39) C
A has double and single bonds.
B has double and single and triple bonds b/w Carbon atoms
C has all double bonds b/w Carbon atoms, and hence all belong to the same homologous series.
D also has varying single and double bonds b/w varying elements.

40) B
When an alkene (Double bonds b/w two carbon atoms) links with another alkene, the double bond breaks in both to join with the other alkene, and all the rest of the atoms stay same and undisturbed.

I FEEL SO DUMB AN DSCRAED!

 

[Phoenix Blood]

I FEEL SO DUMB AN DSCRAED!

Why scared?