IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: Saladin on November 23, 2009, 12:38:39 pm
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Hey guys post any doubts on the following topics:
Physics
Chemistry
Mathematics (c1 C2 S1 FP1)
Business
and Biology, with special host nid404
For Edexcel
I will do my best to help you guys out. Please post all your problems. Will be here for another 30 min.
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Please post any questions that you may have on the previously stated subjects.
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Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3 of neon at 1 kPa
pressure.
If the flasks are connected at constant temperature, what is the final pressure?
\
Thanks in advance :)
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when the flasks are connected the total volume of them both is 1+2=3dm3
now using boyle's law
for flask X:p1v1=p2v2
1(2)=p2(3)
p2=0.67kPa
for flask Y:p1v1=p2v2
2(1)=p2(3)
p2=0.67kPa
total pressure=0.67+0.67=1.34kPa
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Thanx a lot slvri, thats the correct answer.
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when the flasks are connected the total volume of them both is 1+2=3dm3
now using boyle's law
for flask X:p1v1=p2v2
1(2)=p2(3)
p2=0.67kPa
for flask Y:p1v1=p2v2
2(1)=p2(3)
p2=0.67kPa
total pressure=0.67+0.67=1.34kPa
Thanks a lot slvri :D
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Please post any problems that you may have with any of the subjects mentioned above. ;D
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Here u go new member k..something
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Hi,
There is something that i can never seem to understand in a stress strain graph....
the difference between the yield point and elastic limit
according to my teacher they are the same thing,
according to the edexcel book:
Yield Point = the point where a small change in stress causes a large change in strain
Elastic Limit = the point up to which a material is elastically deformed
along with that doubt, there seems to be a misconception with the definitions of the words STRENGTH and TOUGHNESS...
i did some reading, and found that toughness is the energy absorbed per unit volume, and stronger materials have a high ultimate tensile stress..
Now, once again resorting to edexcel definitions:
TOUGHNESS = the property of materials to resist plastic deformation. A large amount of force is needed to cause plastic deformation.
STRENGTH = property of materials to absorb large amounts of stress without failure...
those are a bit vague... any clarification would be great
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Yes, this is often something that we all get confused about:
At the elastic limit, the material does not move back to its original limit, but it still moves back a little. Like it gets deformed yes, but it still springs back, and becomes less than the extended length.
But the yield point is the point at which there is no going back. At this point the material shows plastic behavior, as the length to which u extend it remains like that, at this point slide between the molecules occur, as in the cations in the metal slide over each other and cannot go back to its original length, as the metal loses this energy as heat.
Now toughness and strength
toughness is basically the ability how much stress is required to get the material to its elastic limit, thus talking about tensile stress.
strength of a material is its ability to resist being necked, thus it is talking about compressive stress.
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Well, You can add biology to that...I will help =)
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Done, changed my first post, gr8 to hav u on da team nis404!
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Done, changed my first post, gr8 to hav u on da team nis404!
the pleasure is mine :)
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hey u guys please post any probs dat u may hav and me and nid will help u out as much as we can! :D
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Yes, this is often something that we all get confused about:
At the elastic limit, the material does not move back to its original limit, but it still moves back a little. Like it gets deformed yes, but it still springs back, and becomes less than the extended length.
But the yield point is the point at which there is no going back. At this point the material shows plastic behavior, as the length to which u extend it remains like that, at this point slide between the molecules occur, as in the cations in the metal slide over each other and cannot go back to its original length, as the metal loses this energy as heat.
Now toughness and strength
toughness is basically the ability how much stress is required to get the material to its elastic limit, thus talking about tensile stress.
strength of a material is its ability to resist being necked, thus it is talking about compressive stress.
Hey, thanks for that :)
if u let me, ill add this which i copied from this website:
Strength refers to resistance to deformation, and also to a large elastic range.
At a point called the yield point, the relationship between stress and strain depart from linear, and the material yields meaning that permanent or inelastic and plastic deformation occur.
Beyond the yield point , less stress is required for a given amount of strain (deformation). This proceeds up to the ultimate tensile strength, which is where uniform elongation is measured. At this point, a tensile specimen begins to 'neck', i.e. the change in cross-section becomes non-uniform.
Also, beyond the ultimate tensile strength, the strain increases without additional stress. If the load is not immediately removed, the material will strain to failure.
Toughness is the resistance to failure or crack propagation. It is somewhat related to strength. Very strong materials will have low toughness, i.e. low tolerance for flaws or defects, i.e. incipient cracks.
Toughness relates to the amount of energy absorbed in order to propagate a crack. Materials with high toughness require greater energy (by virtue of force or stress) to maintain crack propagation. Toughness is described in terms of a stress intensity factor (K)
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PPL THE DUDE IS BAQ
POST ANY DOUBTS AND ME OR NID WILL HELP U ANSA DEM! ;D
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can you plz explain this and as to why they are correct??
The conversion of graphite into diamond is an endothermic reaction (?H = +3 kJ mol–1).
C(graphite) ? C(diamond)
Which statements are correct?
1 The enthalpy change of atomisation of diamond is smaller than that of graphite.
2 The bond energy of the C–C bonds in graphite is greater than that in diamond.
3 The enthalpy change of combustion of diamond is greater than that of graphite
the markin scheme says that all of them are correct..
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and ya explain electropositivity... :)
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Electopositivity is the oppsosite of electronegativity. It is an element's ability to donate electrons electrons. Basically how easily something can donate electrons, and thus shows metallic character. For example, Cs is very electro-positive. It has the best ability to donate electrons. But Chlorine is not electropositive, it is electronegative and will want to pull electrons to itself.
Diamond and Graphite:
In order for this reaction to endothermic, 1 2 and 3 must be true.
2 must be true because the bonds broken (3 c-c) must have a greater bond energy than 4 c-c bonds in diamond, in order for more energy to required than given out, for the reaction to be endothermic. Becasue 3 C-C bonds are broken and 4 C-C bonds are made.
1 therefore must be true because atomisation means turning it into gaseous form, thus breaking 3C-C bonds, thus 1 is the same as 2.
3: An endothermic reaction means the material formed is less stable than its products. Thus, the enthalpy change of burning diamond should be greater than graphite, as diamond is less stable and will lose more energy than graphite.
Hope this asnwers ur q. This is by far one of the hardest qs i have answered.
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Please post probs!
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Please post probs!
lol, you recovered from the Question which i have posted( diamond and graphite) here is another one :P
The density of ice is 1.00 g cm–3.
What is the volume of steam produced when 1.00 cm3 of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101 kPa)?
[1 mol of a gas occupies 24.0 dm3 at 25 °C (298 K) and one atmosphere.]
A 0.267 dm3 B 1.33 dm3 C 2.67 dm3 D 48.0 dm
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Srry I do Edexcel, dont have gas Laws.
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Srry I do Edexcel, dont have gas Laws.
np dude :)
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yur so helpful : )
i hav one Q - in Chemistry !
wats electronegativity :s ?
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Basically the ability of atoms to attrat electrons. Every atoms has a number, deonting it's electronegativity - it's ability to attract electrons. The most electronegative is fluorine, I think -2. My subject is bot chemistry.
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aha! nd how do i know the number ?
By the way , yur right ! its is fluorine but i nvr knew why ?
ok thank you astar : ) that made it clearer
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The density of ice is 1.00 g cm–3.
What is the volume of steam produced when 1.00 cm3 of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101 kPa)?
[1 mol of a gas occupies 24.0 dm3 at 25 °C (298 K) and one atmosphere.]
A 0.267 dm3 B 1.33 dm3 C 2.67 dm3 D 48.0 dm
[/quote]
anyone else???
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the dude ,
since yur doing Physics Edexcel !i jst wana ask yu , is momentum in the new syllabus ?
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NO!
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The density of ice is 1.00 g cm–3.
What is the volume of steam produced when 1.00 cm3 of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101 kPa)?
[1 mol of a gas occupies 24.0 dm3 at 25 °C (298 K) and one atmosphere.]
A 0.267 dm3 B 1.33 dm3 C 2.67 dm3 D 48.0 dm
ig of gas =1/18mol sin 1 mol water weighs 18g
so 1g gas occupies 24/18dm3
V1/T1=V2/T2 so V2=V1*T2/T1=24/18*(323+273)/(25+273)=2.585dm3
For some reason I put 1/18 instead 24/18
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The density of ice is 1.00 g cm–3.
What is the volume of steam produced when 1.00 cm3 of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101 kPa)?
[1 mol of a gas occupies 24.0 dm3 at 25 °C (298 K) and one atmosphere.]
A 0.267 dm3 B 1.33 dm3 C 2.67 dm3 D 48.0 dm
1g of gas =1/18mol since 1 mol water weighs 18g
so 1g gas occupies 24/18dm3
V1/T1=V2/T2 so V2=V1*T2/T1=1/18*(323+273)/(25+273)=0.1119dm3
Thanks for the reply but your answer sir is non of the choices given plus we are supposed to use PV=nRT
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I corrected my earlier post