Ideal gases are those that obeys the laws of gases at all temperature and pressures.
But what are real gases? Any examples
Is H2 a real gas or an ideal gas?
All gases are real gases. Ideal gases are only a theoretical model. When you use PV=nRT, you should be aware your calculations are based on ideal gas behaviour, and therefore your calculations are not totally accurate. For more accurate calculations, you'll have to consider many other variables in your calculations, and use more complicated formulae that is beyond 'A' levels.
Originally posted by UltimaOnline:All gases are real gases. Ideal gases are only a theoretical model. When you use PV=nRT, you should be aware your calculations are based on ideal gas behaviour, and therefore your calculations are not totally accurate. For more accurate calculations, you'll have to consider many other variables in your calculations, and use more complicated formulae that is beyond 'A' levels.
Yep there's the answer.
Basically PV=nRT was drawn up to show the main 5-6 factors that affect gases.
Help needed for the question: [A-level Nov 10/11]
In a calorimetric experiment 1.60 g of a fuel is burnt. 45 % of the energy released is absorbed by 200 g of water whose temperature rises from 18 °C to 66 °C. The specific heat capacity of water is 4.2 J /g /K.
What is the total energy released per gram of fuel burnt?
Solution:
q= mc deltaT
q= 200 x 4.2 x 48 = 40320 J.................energy released
Now from this 40320J 45% is absorbed by water means 18144J
total energy release/ gm = 40320/1.6 = 25200J
But the answer is 56000J!!
entropy of it is used in gas turbine stage calculations.
or is it enthalpy
Hi Kahynickel,
you got the concept right that Q=mc DeltaT.
But you misunderstood the question.
Now Q=mc DeltaT = 200 x 4.2 x 48 = 40320 J
This energy is the energy absorbed by the water and it constitutes only 45% of the total energy released.
Total energy released = 100/45 X 40320 J = 89600 J
=> energy released per g = 89600/1.6 = 56000J .
anybody knows where to get gas turbine worked examples on internet?
Hi Hoay,
The ideal gas equation pV = nRT is a model (obtained from experimental facts) that physicists use to approximate behaviour of real gases at extremely low pressures and high temperatures. In other words, all real gases at such conditions (low pressures and high temperatures) tend to become ideal gases and can reasonably be modelled by the ideal gas equation. Fortunately, as UltimaOnline said, real gases and their corresponding models are not in the H2 syllabus.
PhdGuy you are saying that the total energy released has not been given in question. 40320J is the 45% of the total energy that is absorbed by water. Total energy (T.E) hence is:
45% of T.E = 40320
45/100 T.E = 40320
T.E = 40320 x 100/45 = 89600J
How many isomers with the formula C5H10 have structures that involve π bonding?
A 3 B 4 C 5 D 6
Ans. Pentene 1 Structure H2C=CH-CH2-CH2-CH3
Pent-2-ene Two structures cis and trans
2-methyl-but-2-ene 1structure
So 4 structures are possible but D is the answer.
Originally posted by hoay:How many isomers with the formula C5H10 have structures that involve π bonding?
A 3 B 4 C 5 D 6
Ans. Pentene 1 Structure H2C=CH-CH2-CH2-CH3
Pent-2-ene Two structures cis and trans
2-methyl-but-2-ene 1structure
So 4 structures are possible but D is the answer.
You missed out two other possible terminal alkenes (ie. structural isomers with no geometric isomers).
Originally posted by Kahynickel:PhdGuy you are saying that the total energy released has not been given in question. 40320J is the 45% of the total energy that is absorbed by water. Total energy (T.E) hence is:
45% of T.E = 40320
45/100 T.E = 40320
T.E = 40320 x 100/45 = 89600J
That's right.
Thank you very much for the clue. I finally got them
You mean 3-methylbutene CH2=CH-CH(CH3)2
and 2-methylbutene CH3CH2-C(CH3)CH2
I have made different combinations but failed to draw the last. After concentrating on the structural isomers term that you described I got them right.
Is there any short way to get the number of different isomers for a given molecular formula?
For A-level chemistry calculations of all types simple and challenging which book you would recommend. Thank you.
No, there is no shortcut formula for "structural isomer" questions. You have to draw them all out one by one.
For stereoisomers, the maximum number is 2^n, where n = no. of chiral carbons and alkene double bonds (that are capable of geometric isomerism, ie. terminal alkene double bonds excluded). But beware of meso compounds.
But more challenging questions will combine both structural isomers and stereoisomers, so you've no choice but to work them all out manually.
Regarding your query on chemistry calculation questions, refer to my website for the list of books.
CS Toh's Practice Questions book and MCQ book, as well as the RJC (Chan Kim Seng) book and the HCJC (George Chong) book, will cover the simple to intermediate difficulty levels.
For more challenging questions (particularly on the chemical equilibria, acid-base equilibria, solubility equilibria topics), you can use the various University level books, such as "Chemical Principles" (free online ebook), and "Exploring Chemical Analysis".
More info on all books mentioned are on my website :
http://infinity.usanethosting.com/Tuition/#Books_for_H2_Chemistry
The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.
What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24
I have no idea what to do next.......... except to form an equation:
1 = x+0.5+y
Please help.
Originally posted by hoay:The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24
Start by drawing these 3 smaller hydrocarbon products and piece them together like a jigsaw puzzle. Based on the fact that the longest hydrocarbon obtained is only 3 carbons, obviously the original large alkane must be branched. Based on the fact that 50% of the products are ethene, that means two of the four branches must be ethyl groups. The third branch must be the propyl group. The intersection of the branches, itself generates methane.
Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine
D is the answer.
But Chlorine is a gas how we are supposed to consider it in solid state?? Sulphur is a solid having S8 molecules chlorine is a gas Cl2. Please elaborate.
Originally posted by hoay:Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine
D is the answer.
But Chlorine is a gas how we are supposed to consider it in solid state?? Sulphur is a solid having S8 molecules chlorine is a gas Cl2. Please elaborate.
A - metallic vs covalent
B - covalent vs van der Waals
C - metallic vs covalent
D - covalent and covalent
Organic compound containing flourine and chlorine are commercially important. I have mentioned some of their properties and the reason associated with that use.
Anaesthetic: Since they are inert.
Deodorants/Aerosoul propellants: due to their volatility.
Solvents: due to their volatility
PVC: Due to its inertness
Fire extinguishers: Due to their inertness
Refrigerants: Due to their low boiling points.
Please make any corrections.
Originally posted by hoay:Organic compound containing flourine and chlorine are commercially important. I have mentioned some of their properties and the reason associated with that use.
Anaesthetic: Since they are inert.
Deodorants/Aerosoul propellants: due to their volatility.
Solvents: due to their volatility
PVC: Due to its inertness
Fire extinguishers: Due to their inertness
Refrigerants: Due to their low boiling points.
Please make any corrections.
Your answers are ok.
Group II sulfates exists in difefrent crystlaline forms. MgSO4, CaSO4 have different number of water molcecules attached to them.
Please explain this.
Originally posted by hoay:Group II sulfates exists in difefrent crystlaline forms. MgSO4, CaSO4 have different number of water molcecules attached to them. Please explain this.
Different ionic radii and different charge densities of the cation, results in different coordination numbers, different ionic crystal lattice structures, different ion-ligand geometries, and different polymeric hydrate structures, further complicated by different geometrical structures of hydrogen bonding, both between the water molecules themselves, as well as between the water molecules and the anions.
In order words, this is a highly complex matter that requires a depth of discussion significantly beyond 'A' levels.
If you're asking this question at 'A' levels (either coz you're a student or a tutor), then understand that this quesiton cannot be adequately handled at 'A' levels, and whichever JC (or even if it's Cambridge) asks this question in an 'A' level exam, deserves a kick up the ass.
If you're asking this question at any level higher than 'A' levels, then this is not a suitable forum to ask such questions. Chemistry questions beyond 'A' levels should be discussed on ChemicalForums.com.
The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.
What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24
UltimaOnline replied:
Start by drawing these 3 smaller hydrocarbon products and piece them together like a jigsaw puzzle. Based on the fact that the longest hydrocarbon obtained is only 3 carbons, obviously the original large alkane must be branched. Based on the fact that 50% of the products are ethene, that means two of the four branches must be ethyl groups. The third branch must be the propyl group. The intersection of the branches, itself generates methane.
Based on this help I have come up with this structure:
CH2-CH3
CH3-C-CH2-CH3
CH2-CH3
Is it possible to calcultae the remaining mole fraction of mentahne and propene from the data given. Since they both will be 0.5- (x+y) = 1.