How do you do this Chemistry question?

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glorydayes365
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Can anyone help me explain each answer A B C and D, why is that and why is that not the answer.
Thank you.

Answer is D by the way.
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charco
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(Original post by glorydayes365)
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Can anyone help me explain each answer A B C and D, why is that and why is that not the answer.
Thank you.

Answer is D by the way.
What's YOUR take on each of the statements?
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RtheBotanist
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A: Chlorine actually gives a higher bond enthalpy than iodine, because a chlorine is more electronegative = stronger attraction to electrons in the bond.
B: The statement is correct, but that fact would predict that the more polar C-Cl bond would be better at attracting the nucleophilic OH- ions, leading to higher rate of reaction with chlorine.
C:Plain wrong. C-Cl is more polar due to chlorine's electronegativity, so it has larger + and - charges.
D:The key is that because iodine creates less polarity, it forms a weaker bond which can be broken off with less energy. This outweighs the effect of decreased charge on the adjacent carbon. The thing is, there's no way we students could actually work out which is a larger factor, so we just have to memorise that it is the case.

C and D are the only answers that could be logically applied as an explanation for the increased rate if we assume the statements are true. C is an incorrect fact though, so the answer has to be D.

Essentially, its a nasty question conceptually as its entire premise is you having memorised that for these reactions, bond enthalpy is more important than bond polarity. However by process of elimination of wrong or unapplicable statements you can arrive at D anyway.
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glorydayes365
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(Original post by RtheBotanist)
A: Chlorine actually gives a higher bond enthalpy than iodine, because a chlorine is more electronegative = stronger attraction to electrons in the bond.
B: The statement is correct, but that fact would predict that the more polar C-Cl bond would be better at attracting the nucleophilic OH- ions, leading to higher rate of reaction with chlorine.
C:Plain wrong. C-Cl is more polar due to chlorine's electronegativity, so it has larger + and - charges.
D:The key is that because iodine creates less polarity, it forms a weaker bond which can be broken off with less energy. This outweighs the effect of decreased charge on the adjacent carbon. The thing is, there's no way we students could actually work out which is a larger factor, so we just have to memorise that it is the case.

C and D are the only answers that could be logically applied as an explanation for the increased rate if we assume the statements are true. C is an incorrect fact though, so the answer has to be D.

Essentially, its a nasty question conceptually as its entire premise is you having memorised that for these reactions, bond enthalpy is more important than bond polarity. However by process of elimination of wrong or unapplicable statements you can arrive at D anyway.
Thank you so much for your very detailed answer. This helped me to look at which area to study more on because they always make the MC questions super difficult when it seems “simple”. Thanks again.
And yea I was thinking that C seems off.
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charco
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(Original post by RtheBotanist)
A: Chlorine actually gives a higher bond enthalpy than iodine, because a chlorine is more electronegative = stronger attraction to electrons in the bond.
B: The statement is correct, but that fact would predict that the more polar C-Cl bond would be better at attracting the nucleophilic OH- ions, leading to higher rate of reaction with chlorine.
C:Plain wrong. C-Cl is more polar due to chlorine's electronegativity, so it has larger + and - charges.
D:The key is that because iodine creates less polarity, it forms a weaker bond which can be broken off with less energy. This outweighs the effect of decreased charge on the adjacent carbon. The thing is, there's no way we students could actually work out which is a larger factor, so we just have to memorise that it is the case.

C and D are the only answers that could be logically applied as an explanation for the increased rate if we assume the statements are true. C is an incorrect fact though, so the answer has to be D.

Essentially, its a nasty question conceptually as its entire premise is you having memorised that for these reactions, bond enthalpy is more important than bond polarity. However by process of elimination of wrong or unapplicable statements you can arrive at D anyway.
I am not comfortable with you explaining bond strength purely on the basis of electronegativity (difference). It IS a factor, but not the only factor.

C-C bond strength = 346 kJ
C-Cl bond strength = 324 kJ
C-H bond strength = 414 kJ

There is also correlation with atomic radius.This can be seen by looking at the bond enthalpies of the halogens:

Cl-Cl bond enthalpy = 242 kJ
Br-Br bond enthalpy = 193 kJ
I-I bond enthalpy = 151 kJ

BUT F-F is an exception = 159 kJ (supposedly "explained" by inter-electron repulsion at close range)
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glorydayes365
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(Original post by charco)
What's YOUR take on each of the statements?
My explanation wouldn’t be understood by others 😂😂😂 so I asked for help
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glorydayes365
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(Original post by charco)
I am not comfortable with you explaining bond strength purely on the basis of electronegativity (difference). It IS a factor, but not the only factor.

C-C bond strength = 346 kJ
C-Cl bond strength = 324 kJ
C-H bond strength = 414 kJ

There is also correlation with atomic radius.This can be seen by looking at the bond enthalpies of the halogens:

Cl-Cl bond enthalpy = 242 kJ
Br-Br bond enthalpy = 193 kJ
I-I bond enthalpy = 151 kJ

BUT F-F is an exception = 159 kJ (supposedly "explained" by inter-electron repulsion at close range)
Chemistry debate 😵
How are both of you so smart 😢
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charco
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(Original post by glorydayes365)
Chemistry debate 😵
How are both of you so smart 😢
Understanding chemistry doesn't make you "smart".
It simply means that you understand chemistry - you can be a total tea-cake in every other domain.
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