Chemistry MCQ thread...

[aquariangurl]

YEAH, Omg Thanx dude!

 

[MHHaider707]

all A, B, C and D have high melting point.

- graphite is an allotrope of carbon ( meaning the same element of different form )
- Aluminium chloride dissolves in water to give a very acidic solution / magnesium chloride dissolves partially water / chloride of lead and CCl4 do not dissolve in water
- aluminium oxide is insoluble in water / magnesium oxide and lead (II) oxide dissolve in water to give alkaline solution / CO2 dissolves partially in water to give an acidic solution.

ok?

yeah its best explanation of this Q!!!

 

[xHazeMx]

Flask X contains 1dm3 of helium at 2 kPa pressure and flask Y contains 2dm3 of neon at 1 kPa
pressure.
If the flasks are connected at constant temperature, what is the final pressure?
A 1 1/3 kPa B 1 1/2 kPa C 1 2/3 kPa D 2kPa

what could be the answer and why?

 

[MHHaider707]

answer A???

 

[xHazeMx]

yeah .. how did u get it? the p1v1 = p2v2 equation ? ..

 

[Xthegreat]

according to boyle's law, p1v1 = p2v2

so when the 2 flask connect together, the total volume is now 1 + 2 = 3dm3
using the formula above , for flask X
- 1 x 2 = p x 3
- p = 2/3
for flask Y
- 2 x 1 = p x 3
- p = 2/3
therefore, the total pressure after both flask connect is 2/3 + 2/3 = 4/ 3
so answer is A.

 

[xHazeMx]

oh how i didnt think about that .. thanks alot

 

[xHazeMx]

Which statement about the standard enthalpy change of formation of carbon dioxide is correct?

A It is equal to the standard enthalpy change of combustion of carbon.

B It is equal to twice the bond energy of the C=O bond.

C It is the energy released when one mole of carbon dioxide is formed from carbon at the
temperature of combustion of the carbon.

D It is the same for carbon dioxide produced from graphite and from diamond.

its A but why it is not C ?!

 

[MHHaider707]

yeah .. how did u get it? the p1v1 = p2v2 equation ? ..

Yeah!!

 

[MHHaider707]

Which statement about the standard enthalpy change of formation of carbon dioxide is correct?

A It is equal to the standard enthalpy change of combustion of carbon.

B It is equal to twice the bond energy of the C=O bond.

C It is the energy released when one mole of carbon dioxide is formed from carbon at the
temperature of combustion of the carbon.

D It is the same for carbon dioxide produced from graphite and from diamond.

its A but why it is not C ?!

I think in C it states that carbon dioxide is formed by carbon but did not stated that it is formed by constituent elements i-e carbon and oxygen so that's why C is wrong!!!!

 

[Zishi]

so ready for a tough one ZiShi....

It's C.

And for the other question. The answer is graphite.

 

[xHazeMx]

Which statement about the standard enthalpy change of formation of carbon dioxide is correct?

A It is equal to the standard enthalpy change of combustion of carbon.

B It is equal to twice the bond energy of the C=O bond.

C It is the energy released when one mole of carbon dioxide is formed from carbon at the
temperature of combustion of the carbon.

D It is the same for carbon dioxide produced from graphite and from diamond.

its A but why it is not C ?!

I think in C it states that carbon dioxide is formed by carbon but did not stated that it is formed by constituent elements i-e carbon and oxygen so that's why C is wrong!!!!

combustion means that it reacts with oxygen so i dont get it why C is wrong though i know the answer is A

 

[MHHaider707]

Which statement about the standard enthalpy change of formation of carbon dioxide is correct?

A It is equal to the standard enthalpy change of combustion of carbon.

B It is equal to twice the bond energy of the C=O bond.

C It is the energy released when one mole of carbon dioxide is formed from carbon at the
temperature of combustion of the carbon.

D It is the same for carbon dioxide produced from graphite and from diamond.

its A but why it is not C ?!

I think in C it states that carbon dioxide is formed by carbon but did not stated that it is formed by constituent elements i-e carbon and oxygen so that's why C is wrong!!!!

combustion means that it reacts with oxygen so i dont get it why C is wrong though i know the answer is A

no idea then!!! :%)

 

[Xthegreat]

Which statement about the standard enthalpy change of formation of carbon dioxide is correct?

A It is equal to the standard enthalpy change of combustion of carbon.

B It is equal to twice the bond energy of the C=O bond.

C It is the energy released when one mole of carbon dioxide is formed from carbon at the
temperature of combustion of the carbon.

D It is the same for carbon dioxide produced from graphite and from diamond.

its A but why it is not C ?!

I think in C it states that carbon dioxide is formed by carbon but did not stated that it is formed by constituent elements i-e carbon and oxygen so that's why C is wrong!!!!

C is wrong because it is formed at the temperature of combustion of the carbon!!! it should be at STANDARD CONDITIONS, 25'c , 1atm!!!

 

[xHazeMx]

yeah thats correct ! .. i got it now !

 

[sakibfaiyaz]

Guys the answer to this one is A
could you please tell me how it is polar? :S

 

[xHazeMx]

the difference in electronegativities of S and O, O and Na, C and O makes it polar as they have different electronegativities. it is water attracting because it forms hydrogen bonds with water molecules

 

[Zishi]

Guys the answer to this one is A
could you please tell me how it is polar? :S

It is polar because of electronegativity difference between sulfur and oxygen atoms.

 

[sakibfaiyaz]

But, doesnt polarity depend upon 'net dipole moment'? Sulfur has an equal dipole moment on either side both horizontally and vertically (as the differences in electronegativities between S and O remain constant), so doesn't this symmetry cancel out its net dipole moment? :S

 

[xHazeMx]

thats correct but look to (1) it says (PART) of the structure is polar which is the ONa part, O and Na have different electronegativities