Chemistry: Post your doubts here!

[h4rriet]

Two moles of compound P were placed in a vessel. The compound P was partly decomposed by heating. A dynamic equilibrium between chemicals P, Q and R was established.
At equilibrium, x mol of R were present and the total number of moles present was (2 + x).
What is the equation for this equilibrium?
A P 2Q + R
B 2P 2Q + R
C 2P Q + R
D 2P Q + 2R
I need help in this question as well !

You'll have to draw an ICE chart for the equations in A, B, C and D. Here's the one for B:

 

[strangerss]

hwo come an ideal gas's volume is not inversely proportional to it's pressure??

 

[cute97]

Q.4:
N2+O2--->2NO
180+(-994)+(-494)= 2X
X=655 hence A.

Thank you can u do the other two plz

 

[h4rriet]

I have a couple of questions I don't really understand, could anybody help?

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That's not a couple!
Anyway, for the first: you're taking the Kc for the reverse reaction, so you'll take the reciprocal of the forward reaction. Then, look at reaction II, and you'll see that all the moles have been divided by 2. Therefore you take the square root of the reciprocal of the Kc.
The second: AlCl3 is entirely covalent. MgCl2 is very slightly acidic in solution, so it is covalent to a limited degree.
The 3rd: Ammonium compounds give off ammonia when reacted with a base. You have to recognise D to be ammonium nitrate: NH4NO3. They've just jumbled the atoms in the compound.
The 4th: Perhaps it'll help if you point out which option (1/2/3) you're having trouble with.
5th: Don't look at the 2D shape. Count the bond pairs and lone pairs and write down the angles.

 

[h4rriet]

hwo come an ideal gas's volume is not inversely proportional to it's pressure??

It is.

 

[Dr.MMM]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q28?

 

[Jiyad Ahsan]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q4 h4rriet

96 kg hydrogen is left means (120 - 96) = 24 kg was used up

The equation:
3H2 + N2 --> 2NH3

(3 x 2) = 6 kg hydrogen produces (2 x 17) = 34 kg ammonia

1 kg hydrogen would produce (34/6) kg ammonia
24 kg hydrogen would produce
= (34 / 6) x 24
= 136 kg ammonia

That is why answer is C

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf can some one explain Q11 please??

For 11, n has to be the number of bonds in the compound. For example, the bond energy of a C-H bond is found by divided the enthalpy of formation of CH4 by 4, because there are 4 C-H bonds in CH4.

 

[HubbaBubba]

That's not a couple!
Anyway, for the first: you're taking the Kc for the reverse reaction, so you'll take the reciprocal of the forward reaction. Then, look at reaction II, and you'll see that all the moles have been divided by 2. Therefore you take the square root of the reciprocal of the Kc.
The second: AlCl3 is entirely covalent. MgCl2 is very slightly acidic in solution, so it is covalent to a limited degree.
The 3rd: Ammonium compounds give off ammonia when reacted with a base. You have to recognise D to be ammonium nitrate: NH4NO3. They've just jumbled the atoms in the compound.
The 4th: Perhaps it'll help if you point out which option (1/2/3) you're having trouble with.
5th: Don't look at the 2D shape. Count the bond pairs and lone pairs and write down the angles.

Thanks for answering all those questions! My main problem in the fourth question is that I don't understand how it can produce two alkenes? I understood the third option though.

 

[Saad (سعد)]

وعليكم السلام
7 and 11:
Draw ICE charts, i.e. initial moles, change in moles and equilibrium moles, for ALL the options (A, B, C and D). Then see which one has x + 2/x for its final moles.
For example, 7 D:

We divide the equilibrium moles by 2 because the question says that the final moles of R are x, so we need to make the final moles of R = x.

Jazak Allah Khayr!

 

[Saad (سعد)]

Question 14, please.

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

 

[h4rriet]

Thanks for answering all those questions! My main problem in the fourth question is that I don't understand how it can produce two alkenes? I understood the third option though.

When an alcohol is dehydrated, the -OH is eliminated and an H atom from a neighbouring C atom.

 

[HubbaBubba]

When an alcohol is dehydrated, the -OH is eliminated and an H atom from a neighbouring C atom.

Thank you, it makes much more sense now! If I could like your posts more than once, then I would

 

[h4rriet]

Question 14, please.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

When you write the equation for the decomposition of a Group II metal nitrate, you see that the mole ratio of the metal nitrate to the metal oxide is 1:1. So n(nitrate)=n(oxide). You have the mass of the nitrate and you can find the mass of the oxide (mass of nitrate minus mass of gases). You can calculate the molecular mass of Group II metal nitrate and oxide knowing the general formulae: M(NO3)2 and MO. M can be x. Cross multiply.

 

[HongYue]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
Question 7, 18, 20, 24.
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Question 2,9, 21, 22 ,38
Thx In advance !

 

[kiran11]

please explain q 24
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

 

[kiran11]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
Question 7, 18, 20, 24.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Question 2,9, 21, 22 ,38
Thx In advance !

for q 18 see the atomic radius and ionic radius graphs from any book for period 3, u shud memorise it
for q 20 the products formed are CH3COONa and C3H7OH , find there molecular mass, and then percentage by mass
for 7 i did 2+x=2+x/2 (but this may not b right way, anywyz i got my ans correct)

 

[Dr.MMM]

A reaction which causes the presence of oxides of nitrogen in car exhausts is the formation of
NO.
N2 + O2→ 2NO ∆H = +180kJmol–1
What is the bond energy in kJmol–1 of the bond between the atoms in NO?
A 655 B 835 C 1310 D 1670

PLEASE SOLVE AND EXPLAIN THIS QUESTION!

 

[Aries_95]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q.17 plz!
h4rriet

 

[darkxangel]

The reaction between aluminium powder and anhydrous barium nitrate is used as the propellant
in some fireworks. The metal oxides and nitrogen are the only products.
Which volume of nitrogen, measured under room conditions, is produced when 0.783 g of
anhydrous barium nitrate reacts with an excess of aluminium?
A 46.8cm3
B 72.0cm3
C 93.6cm3
D 144cm3
Help !