Gchem

[Glycogen]

---

Members do not see this ad.

Calculate the bond energy of a BrF bond using the following reaction equation. deltaH of BrF5= -429 kJ/mol
deltaH of Br = 112 kJ/mol
deltaH of F= 79 kj/mol

Br (g)+ 5F (g)--->BrF5 (g)

a.936 kj/mol
b.187 kj/mol
c.86 kj/mol
d.47 kj/mol

I really don't get this.It is either super easy or super hard.Would you explain ur answer please.
Thanks.

 

[klutzy1987]

Answer is C. They tell you that the deltaH for BrF5 is -429. Therefore since that is composed of 5 BrF bonds each individual bond has about 429/5 or 86 kj of energy. Unless i am reading something wrong here that should be right.

 

[shoombol tallah]

yeah i got c too but that seems a little too simple lol. Whats the answer?

 

[Glycogen]

No,the right answer is B.Even by reading the explanation,I can not get it.

 

[klutzy1987]

No,the right answer is B.Even by reading the explanation,I can not get it.

HUH?? i must be missing something or it must be from Kaplans. Can you post the explanation for the answer please i am curious.

 

[PooyaH]

Yeah, the answer is C. The deltaH's for Br, and F are useless info for this question. All you need is the bond energy of BrF. and since BrF5 = -429KJ/mol, just divide it by 5 and you get the BrF bond energy.

 

[harrygt]

The answer is "B".
You have to calculate the dH of the reaction first using the dH formation of each compound.
remember: there are two formulas for calculating dH. one is subtracting sum of dH formation of reactants from products [dH pro. - dH react.]
The other is subtracting the binding energy of products from reactants [bind. energy of reactants - bind. energy of products]

Do the first calculation first, using the provided numbers. You will get dH = -936.
Then use the second equation [there is obviously no binding energy on the reactant side]. You will finally end up dividing 936 by 5 to find the binding energy of F-Br = 187
I hope this is clear.

 

[klutzy1987]

I know wht they did to get their answer but that is ludicrous. To get 187 you have to do -429-(heat of reactants)=936
Then -936/5=187.2

That is wrong though so i do not get it. Maybe the answers explained will be better. Or it is from kalpans in which case it makes sense. Kaplans sucks because it is full of mistakes.

 

[harrygt]

I know wht they did to get their answer but that is ludicrous. To get 187 you have to do -429-(heat of reactants)=936
Then -936/5=187.2

That is wrong though so i do not get it. Maybe the answers explained will be better. Or it is from kalpans in which case it makes sense. Kaplans sucks because it is full of mistakes.

Bro, I agree that Kaplan sux to some degree, but don't blame this one on Kaplan though. The correct answer is "B", and it is not "ludicrous."

 

[klutzy1987]

The answer is "B".
You have to calculate the dH of the reaction first using the dH formation of each compound.
remember: there are two formulas for calculating dH. one is subtracting sum of dH formation of reactants from products [dH pro. - dH react.]
The other is subtracting the binding energy of products from reactants [bind. energy of reactants - bind. energy of products]

Do the first calculation first, using the provided numbers. You will get dH = -936.
Then use the second equation [there is obviously no binding energy on the reactant side]. You will finally end up dividing 936 by 5 to find the binding energy of F-Br = 187
I hope this is clear.

But they tell you the individual energy for BrF5 in which case you do not care about nything else. If you know the energy of BrF5, then that divided by 5 will give you the energy of the individual bonds. So if BrF5 is -429 and there are 5 equal bonds that make up BrF5 then each individual bond is going to be a fifth of that or will be 87. I dont see why you should do it like you said. That would make no sense.

 

[Glycogen]

The answer is "B".
You have to calculate the dH of the reaction first using the dH formation of each compound.
remember: there are two formulas for calculating dH. one is subtracting sum of dH formation of reactants from products [dH pro. - dH react.]
The other is subtracting the binding energy of products from reactants [bind. energy of reactants - bind. energy of products]

Do the first calculation first, using the provided numbers. You will get dH = -936.
Then use the second equation [there is obviously no binding energy on the reactant side]. You will finally end up dividing 936 by 5 to find the binding energy of F-Br = 187
I hope this is clear.

See,I called you the king of chemistry once and you truly are.Yes,but this stupid Kaplan explained it in 10 lines which caused me more confusion.Harry would you tell me why we have to divided by 5.it says that there is no bond broken in the reaction!!!

 

[klutzy1987]

Actually i think i change my mind Bond energy is not the same as Delta H. That was my mistake lol. Good thing i finished and dont really care if i make a mistake anymore lol. Harry is right though at least i think he is.

 

[osimsDDS]

yea im with harry, you have to calculate the dH of rxn which is 936 then divide by 5 cuz there are 5 bonds so you get B, 187 about...

 

[harrygt]

See,I called you the king of chemistry once and you truly are.Yes,but this stupid Kaplan explained it in 10 lines which caused me more confusion.Harry would you tell me why we have to divided by 5.it says that there is no bond broken in the reaction!!!

lol, you are funny man [talking about the chem king stuff]

there is no bonds broken in the reactants, but there are 5 bonds in BrF5, therefore you have
0 - 5[Br-F] = -936

then you get Br-F = 187.😉

 

[klutzy1987]

Way to do this is to first calculate the Bond energy of the entire reactionwhich is the same as the delta H. The delta H here is -936kj. Then take that and plug it into the bond dissociation formula i.e. (Bonds Broken)- (bonds formed). Over here there are no bonds broken so the bonds formed= 936. Now just break it down to the individual bonds formed and you get that there are a total of 5 bonds Br-F formed and together they equal 936. Therfore individually they equal 187. Good thinking Harry.