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Chemistry: Post your doubts here!

B

Browny

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http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Can anybody please explain questions 22, 31? Ans are A and B respectively.

In 22 why can't B be the correct answer and in 31 can you explain the 1 statement.
Also in a reaction pathway involving a intermediate is the first stage Ea always greater than the second stage Ea?

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
Can anybody please explain questions 5, 19? Ans are B and B respectively.

THANKS IN ADVANCE!:)
 
K

kanchan dhiman

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Namehere said:
Here you need to know two concepts/formulas:
mole fraction = number of moles of molecule A / total number of moles
Partial pressure of A = mole fraction of A x total pressure

If 20% of steam had been converted to hydrogen and oxygen, there must be 80% of steam left. So, if you before had 1 mole of steam, you now have 0.8 moles of steam (80% of 1.). Because of the 2:2:1 ratio in the equation, 2H2O ---> 2H2 + O2 , if 0.2 moles of steam had been converted into its products, then by simple stoichiometry the change for H2 is +0.2 and for O2 +0.1.

So you now have the moles of each substance present at equilibrium. If you now use the formulas from the beginning, to calculate the partial pressure, you would see you need the mole fraction of your gas and the total pressure. So, mole fraction = number of moles of molecule A / total number of moles

For steam, you have 0.80 moles, for H2 0.20 and for O2 0.10. If you add them up this give 1.1 - the total number of moles. Therefore, the mole fraction of steam is 0.80/1.1, for H2 is 0.20/1.1 and for O2 is 0.10/1.1. To get the partial pressure of each gas you now times the mole fraction of each substance by the total pressure at which the experiment is done - 1 atm. Hence for steam the partial pressure is 0.8 x 1 / 1.1 and so on...

Hope it helps.
Click to expand...
How do you get mole of H2 and O2 please explain?????
 
S

Snowysangel

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not.maria said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

can anyone kindly explain:
q6 10 11 23 26
Click to expand...
6:B because the graph will move to the left with its peak becoming higher (hence A will move up) but to maintain the number of particles, B and C will have to move down because the number if particles having a lower energy will increase and those having higher energies will decrease
10:C draw up ratios. The number of atons of and percentages of O,H and Ca are already given to you. The percentage divided by the number if atoms will always give a co start value. Find that value and equate it to the ratio of the percentages & number of atoms of the other atoms. You'll end up with he same answer for both Si and Al ie 3
 
sweet.sugar

sweet.sugar

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http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Q1-c
i got D cz pb(c2h5)4 +o2 -->pbo + co2
2*4=8 c and 5*4=20h on react side so if we balance i got 8 oxy frm co2 and 10 oxygens from h2o n 1 oxy from pbo total 27 :/
Q4-c (explain it)
Q6-a (h2=hr-h1 so -395+297=-98 so y is it a ?)
Q12-d (i wrote the eq n for mg n s it is 1 mol of o2 n for al it is 3 moles (3o2) so y is the curve for s the highest ie ans shud be c ) :/
Q20-b (plz write the isomers )
Plz help :)
 
ZaqZainab

ZaqZainab

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I

IGCSE13

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ZaqZainab

ZaqZainab

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