Chemistry MCQ thread...

[meoooow]

hii, :Search:
i need help with these!

 

[MHHaider707]

A mixture containing 0.100 mol of CaCO3 and 0.100 mol of CaO are introduced
into an evacuated 0.01 m3 vessel. The vessel is heated to a constant
temperature of 385 K such that the equilibrium below is established.
CaCO3(s) CaO(s) + CO2(g)
The partial pressure of carbon dioxide at equilibrium is then found to be 0.220
atm.
What is the total mass of CaCO3 at equilibrium after an additional 0.300 atm of
carbon dioxide is pumped into the vessel?
A 0.530 g
B 10.0 g
C 12.5 g
D 19.5 g

Answer is C!!

 

[Zishi]

hii, :Search:
i need help with these!

It'd be good if you take snapshots of your questions by opening the page where the question is located and then pressing the "print screen" button on your keyboard. Then go to paint and press "ctrl+v", you'll get it pasted into Paint. Crop the question and then attach it over here. This way I'll be able to answer all of your questions. I can't open .docx document.

 

[meoooow]

4 Some bond energy values are listed below.
bond bond energy / kJ mol–1
C–H 410
C–Cl 340
Cl–Cl 244
Br–Br 193

These bond energy values relate to the following four reactions.
P Br2 → 2Br
Q 2Cl → Cl2
R CH3 + Cl → CH3Cl
S CH4 → CH3 + H

What is the order of enthalpy changes of these reactions from most negative to most positive?
A P → Q → R → S
B Q → R → S → P
C R → Q → P → S
D S → P → Q → R

i hope this is better!

 

[kakarocks]

hii, :Search:
i need help with these!

For the enthalpy change one its -88Kj i.e option B because 38 - 214 = -176 and -176/2 = -88

For Oxidation numbers its D +4,-4 because in ammonium nitrate one n was in a state of -3 and one in a state of +5 and they both came to +1 so the -3 one changed by by +4 and +5 one changed by -4

 

[meoooow]

5 Given the following enthalpy changes,
I2(g) + 3Cl2(g) → 2ICl3(s) ΔHo = –214 kJ mol–1
I2(s) → I2(g) ΔHo = +38 kJ mol–1
What is the standard enthalpy change of formation of iodine trichloride, ICl3(s)?
A +176 kJ mol–1
B –88 kJ mol–1
C –176 kJ mol–1
D –214 kJ mol–

i really need help with this!

 

[Zishi]

4 Some bond energy values are listed below.
bond bond energy / kJ mol–1
C–H 410
C–Cl 340
Cl–Cl 244
Br–Br 193

These bond energy values relate to the following four reactions.
P Br2 → 2Br
Q 2Cl → Cl2
R CH3 + Cl → CH3Cl
S CH4 → CH3 + H

What is the order of enthalpy changes of these reactions from most negative to most positive?
A P → Q → R → S
B Q → R → S → P
C R → Q → P → S
D S → P → Q → R

i hope this is better!

It's C. S is most positive because all the C-H bonds are being broken. P is slightly less positive because Br-Br bond energy is less than C-H bond energy. Only one options shows this thing, which is C.

 

[kakarocks]

Read above please meoow i mean :S

 

[sakibfaiyaz]

4 Some bond energy values are listed below.
bond bond energy / kJ mol–1
C–H 410
C–Cl 340
Cl–Cl 244
Br–Br 193

These bond energy values relate to the following four reactions.
P Br2 → 2Br
Q 2Cl → Cl2
R CH3 + Cl → CH3Cl
S CH4 → CH3 + H

What is the order of enthalpy changes of these reactions from most negative to most positive?
A P → Q → R → S
B Q → R → S → P
C R → Q → P → S
D S → P → Q → R

i hope this is better!

P has +193..(check the data booklet)
Q has -244 , it has to be exothermic as bonds are only being made
R has -340 KJ.....USE enthalpy change= energy taken in to break bonds- energy given out by bond formation
S has +410...

Now arrange them from most negative to most positive. You will get R<Q<P<S...
therefore C

 

[Zishi]

hii, :Search:
i need help with these!

For the enthalpy change one its -88Kj i.e option B because 38 - 214 = -176 and -176/2 = -88

For Oxidation numbers its D +4,-4 because in ammonium nitrate one n was in a state of -3 and one in a state of +5 and they both came to +1 so the -3 one changed by by +4 and +5 one changed by -4

5 Given the following enthalpy changes,
I2(g) + 3Cl2(g) → 2ICl3(s) ΔHo = –214 kJ mol–1
I2(s) → I2(g) ΔHo = +38 kJ mol–1
What is the standard enthalpy change of formation of iodine trichloride, ICl3(s)?
A +176 kJ mol–1
B –88 kJ mol–1
C –176 kJ mol–1
D –214 kJ mol–

i really need help with this!

He's already answered it. See that "quoted" post.

 

[meoooow]

4 Some bond energy values are listed below.
bond bond energy / kJ mol–1
C–H 410
C–Cl 340
Cl–Cl 244
Br–Br 193

These bond energy values relate to the following four reactions.
P Br2 → 2Br
Q 2Cl → Cl2
R CH3 + Cl → CH3Cl
S CH4 → CH3 + H

What is the order of enthalpy changes of these reactions from most negative to most positive?
A P → Q → R → S
B Q → R → S → P
C R → Q → P → S
D S → P → Q → R

i hope this is better!

P has +193..(check the data booklet)
Q has -244 , it has to be exothermic as bonds are only being made
R has -340 KJ.....USE enthalpy change= energy taken in to break bonds- energy given out by bond formation
S has +410...

Now arrange them from most negative to most positive. You will get R<Q<P<S...
therefore C

OH i get it!! thanks

 

[meoooow]

Read above please meoow i mean :S

yes i did, im sorry, i just joined so its taking me a while to get a hang of this!

 

[kakarocks]

Read above please meoow i mean :S

yes i did, im sorry, i just joined so its taking me a while to get a hang of this!

Well Welcome to Xpf first of all then

 

[sniper7137]

Hey. Can anyone one help me with Q 10 of October November 2008 and Q 6 of May June 2008?

 

[kakarocks]

Kp only effected by tempreture so D for 10

 

[sniper7137]

Why not pressure. Won't + pressure shift the equilibrium to the right. That means more moles of product. So its partial pressure changes and change in partial pressure changes Kp?

 

[mizmoody]

Q1. In leaded petrol dere is an additive composed of Pb,C and H only. This compound contains 29.7% carbon and 6.19% hydrogen by mass.
What is the value of x in the emperical formula PbC8Hx?
A.5 B.6 C.16 D.20

Q2. A household bleach contains NaClO, as its active ingredient. The conc of NaClO in the bleach can be determined by reacting a known amount with aqeous H2O2.

NaClO(aq) + H2O2(qa) ====> NaCl(aq) + O2(g) + H2O(l)

When 25.0 cm3 of bleach is treated with an excess of aqueous H202, 0.0350 mol of Oxygen gas is given off. What is the conc of NaClO in the bleach?
A. 8.75x10-4 mol dm-3
B. 0.700 mol dm-3
C.0.875 mol dm-3
D.1.40 mol dm-3

 

[meoooow]

38 Which structural formulae represent 2,2-dimethylpentane?
1 (CH3)2CHCH2CH(CH3)2
2 (CH3)3CCH2CH2CH3
3 CH3CH2CH2C(CH3)3

 

[kakarocks]

Chapter 7 Learning Outcome c of the Chemistry syllabus " Deduce whether changes in concentration , pressure or temperature or the presence of a catalyst effect the value of the equilibrium constant "

Answer On page 130 of A-level Chemistry Book-1 By Muhammad Ayub

The value of Kc is unaffected by
1-initial concentrations
2-the direction from which the equilbria is approached
3-the pressure in case of gaseous equillibria
4-the catalyst used for the reaction

Detail given below :

Effect of temperature

For exothermic reaction . KC decreases with increase in temperature
For Endothermic Reaction . Kc increases with increase in temperature .

What you are referring to is the "position of equilibria" Which would be effected by pressure . But the "value of equillibria" wont be effected .

I suggest you to get Ayub's both books . You wont need any other book

 

[xHazeMx]

Q1. In leaded petrol dere is an additive composed of Pb,C and H only. This compound contains 29.7% carbon and 6.19% hydrogen by mass.
What is the value of x in the emperical formula PbC8Hx?
A.5 B.6 C.16 D.20

Q2. A household bleach contains NaClO, as its active ingredient. The conc of NaClO in the bleach can be determined by reacting a known amount with aqeous H2O2.

NaClO(aq) + H2O2(qa) ====> NaCl(aq) + O2(g) + H2O(l)

When 25.0 cm3 of bleach is treated with an excess of aqueous H202, 0.0350 mol of Oxygen gas is given off. What is the conc of NaClO in the bleach?
A. 8.75x10-4 mol dm-3
B. 0.700 mol dm-3
C.0.875 mol dm-3
D.1.40 mol dm-3

find the empirical formula for Q 1 and u will gind value of X
Answer for Q 2 is D right ?