chem mcq...

[hassam]

 

[Feelguud77]

The answer is B raiet?

 

[aquariangurl]

B seem right!

 

[hassam]

its C!!!

 

[aquariangurl]

Heck NO!
How can the rate decrease for any catalytic reaction..because the rate is supposed to become constant after the formation of products. Rite?

 

[xHazeMx]

the answer is C ..

 

[xHazeMx]

i think as products are formed, the rate of reaction increases. then when one of the products is used up as a catalyst, the products decreases and the yield becomes less. hence, rate of reaction decreases

 

[aquariangurl]

i think the rate of reaction increases as the products are formed and then it decreases as the products are used up as catalysts .. is it correct?

I dunno, isn't it supposed to be the other way round, if there are catalysts, THEN the reaction occurs *at the steep line in the graph* then when the line becomes straight that's when the reaction is over, But in C why does it decrease?

 

[xHazeMx]

i think the rate of reaction increases as the products are formed and then it decreases as the products are used up as catalysts .. is it correct?

I dunno, isn't it supposed to be the other way round, if there are catalysts, THEN the reaction occurs *at the steep line in the graph* then when the line becomes straight that's when the reaction is over, But in C why does it decrease?

i m gonna search on the internet about autocatalytic reactions because i dont think its mentioned in my chem notes .. i will let u know when i m done

 

[hassam]

guyxx more difficult mcqs on the way dont go anywhere.....

 

[aquariangurl]

C?

 

[xHazeMx]

guyxx more difficult mcqs on the way dont go anywhere.....

answer is A .. right?

 

[hassam]

YEA C is ryt....A is rong...cos A cn only be formed if there was CL2present in there which is not....there is br2 and CL -ve......which cn act as a nucleophile

 

[hassam]

so get ready..that will be a BRAIN TEASER....

 

[hassam]

 

[xHazeMx]

this is one of the questions which i really dont understand

 

[xHazeMx]

can u fully explain this question?

 

[Saturation]

This is messed up!! Anyone care to explain?

 

[hassam]

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:

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

 

[xHazeMx]

WOW! the only thing i didnt understand in this question before was that freaky enthalpy change part which u made it clear now .. thanks