chem mcq...

[Anonymousx3]

This MCQ was removed from the examination, right?
I read something on the ER, saying the statistics were unsatisfactory so it was removed.

And I also have another difficult MCQ (well, I think it is).

http://www.xtremepapers.me/CIE/Internat ... 4_qp_1.pdf

Question 31.

I reaaally don't get it at all. I'd be grateful if someone could explain it!

 

[Feelguud77]

Dude i haven't gotten past the fact that C is right, see, if the products catalyse the reaction then as reaction progresses, gradient increases and then when finished, the slope becomes flat(zero)..............why the sudden decrease?

 

[Feelguud77]

And Anon, the answer to your question is D(1 only) raiet?
Cuz it works by Hess's law, Direct Enthalpy change=Indirect Enthalpy change.

 

[hassam]

4 What is the order of increasing energy of the listed orbitals in the atom of titanium?
A 3s 3p 3d 4s
B 3s 3p 4s 3d
C 3s 4s 3p 3d
D 4s 3s 3p 3d

 

[sparten]

C coz activation energy is reduced...

 

[sparten]

well to say truth it damnn hard.......bt here u go..and edothermic reaction always leads to a less stable product ...think it other way round....and u ll understand that decoposition of product will be exothermic which means it ll be real quick....so remeber...exothermic are the ones that occur quickly leading to a stable product....so here diamond will be less stable...less stable means less energy of atomisation and bond energy lower than graphite....how wud u account for enthlapy change of combustion....well thats the freaky part..

Carbon occurs in two forms: graphite and diamond. The enthalpy of combustion of graphite is -393.5 kJ, and that of diamond is -395.4 kJ

C(graphite) + O2(g) -> CO2(g) DH = -393.5 kJ

C(diamond) + O2(g) -> CO2(g) DH = -395.4 kJ

Calculate DH for the conversion of graphite to diamond

What we want is DH for the reaction:

exothermic rxn leads to a less stable product coz energy is lost in exothermic rxn while in endothermic energy is absorbed so product more stable
C(graphite) -> C(diamond)

C(graphite) + O2(g) -> CO2(g) DH = -393.5 kJ

CO2(g) -> C(diamond) + O2(g) DH = +395.4 kJ

C(graphite) -> C(diamond) DH = +1.9 kJ

 

[sparten]

4 What is the order of increasing energy of the listed orbitals in the atom of titanium?
A 3s 3p 3d 4s
B 3s 3p 4s 3d
C 3s 4s 3p 3d
D 4s 3s 3p 3d

B

 

[BILALrox01]

The answer is C.. since the rate of reaction will decrese once the conc of reactants becomes the limiting factor.

 

[hassam]

ya u r ryt bilal..its juxt like enzymes in biology

 

[alphabravocharlie]

4 What is the order of increasing energy of the listed orbitals in the atom of titanium?
A 3s 3p 3d 4s
B 3s 3p 4s 3d
C 3s 4s 3p 3d
D 4s 3s 3p 3d

The answer is b.

 

[sweetiepie]

how do we rite kc and kp????

 

[thunderingthunder]

For example we have the equation:
CH4+02-->CO2+2H20
THen the Kc for this reaction will be----->
{(co2)(h2o)^2}/{(CH4)(O2)}.....
Geerallyproduct of conc.of products)/(Product of concentration of reactants)
hope u gt it!!

 

[sparten]

how do we rite kc and kp????

kc=[conc of product 1][conc of product 2]/[conc of reactant1][conc of reactant 2]
kp=parial pressure of products by reactants....
if thea are two moles or more of any product or reactant make its conc power

 

[sweetiepie]

thank you..

 

[honeycoveredcookie]

KC = [products]/[reactants.]

KP = p(products) ^ moles / p(reactants) ^ moles.

 

[thunderingthunder]

thank you..

Mention not....

 

[xHazeMx]

how do we rite kc and kp????

CH3CH2OH + CH3COOH -------> CH3COOCH2CH3 + H2O

the number of moles for each compound is 1. Hence,

Kc : [CH3COOCH2CH3] [H2O] / [CH3CH2OH] [CH3COOH]

Kp follows the same procedure but has a different way to express it.

Kp : P(CH3COOCH2CH3) P(H2O) / P(CH3CH2OH) P(CH3COOH)

each compound ^ number of its moles in a reaction

hope u found that useful

 

[sweetiepie]

hmmm how to find chiral centre in a question like how wil know itx 2 or 3 or 4 m jux confused in that???

 

[xHazeMx]

hmmm how to find chiral centre in a question like how wil know itx 2 or 3 or 4 m jux confused in that???

search for the carbon atoms which is bonded to four DIFFERENT atoms or group of atoms. each one is considered as one chiral carbon

 

[sweetiepie]

i know but m asking how wil know the structure is mixed in mcq paper how wil we decide itx 1 or 2 ???