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Topic: Molar Bond Enthalpy question  (Read 7082 times)

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Offline munchkiness

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Molar Bond Enthalpy question
« on: May 12, 2008, 09:21:24 PM »
Back again  ;D

Question:
Write a balanced equation for the reaction of 1 mole of chlorine gas with 3 moles of fluorine gas to give chlorine triflouride gas.

I believe this is the equation: But please correct me if im wrong.

Cl2 + F3 = 2ClF3

Now using this equation and the bond enthalpy values, calculate the bond enthalpy change for the reaction.

Bond                                          Cl - Cl                  F - F              Cl - F
enthalpy/ kJ mol- 1                      +242                   +159                  +174


Now is the 1st step the sum:

+242 kJ + (3 x +159 kJ) = +719 kJ 

and from that, now what do i do?
« Last Edit: May 12, 2008, 10:46:34 PM by munchkiness »

Offline enahs

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Re: Molar Bond Enthalpy question
« Reply #1 on: May 12, 2008, 09:43:57 PM »
Nope.

You do not find just Cl in nature, what is its formula. Likewise you have the formula for fluorine gas wrong.

Offline munchkiness

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Re: Molar Bond Enthalpy question
« Reply #2 on: May 12, 2008, 10:51:01 PM »
Adjusted my previous post to correct possible errors.

not sure wether its correct now or not.




Offline Borek

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Re: Molar Bond Enthalpy question
« Reply #3 on: May 13, 2008, 03:19:21 AM »
Almost the same problem as before. What is F3?
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Offline munchkiness

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Re: Molar Bond Enthalpy question
« Reply #4 on: May 13, 2008, 06:13:00 PM »
ok ,

Cl2 + F2 + ClF3 is the starting equation,

Balanced is it,

Cl2 + 3F2 = 2Cl2F3

Im counting the same amount on each side anyway.


now to calculate the overall enthalpy change.
I know you add the bond values from the left side of the equation 1st.


and then what do i do?

Books make it so complicated its not understandable when you dont have any science background to speak of.

Please bear with me if i sound so stupid, ( i do feel it )

Last chem lesson i had was when i was 13, ( im now 32 ) But i have to get through this part of my course with at least a passing grade to be able to do the courses i want. ( namely anatomy and human biology )


Offline enahs

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Re: Molar Bond Enthalpy question
« Reply #5 on: May 13, 2008, 06:21:58 PM »
Now quite, though it just looks maybe a typo on the balanced line, for the chlorine trifluoride.
Now it is just the sum of the energy of the bonds broken - the sum of the energy of the bonds formed.

See here (http://www.webchem.net/notes/how_far/enthalpy/enthalpy_diagrams.htm) for more details and an example.




Offline munchkiness

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Re: Molar Bond Enthalpy question
« Reply #6 on: May 14, 2008, 09:39:30 PM »
These are the calculations i've done.

Have no idea if they're right,

Cl2 + F2 Form ClF3 (given to me as part of the question)

Balanced equation :

Cl2 + 3F2 = 2ClF3


Enthalpy change:

+242 + (3 x +159 ) - (2 x +174) + 159

= 212 kJ


If i've STILL gone wrong, can someone highlight the incorrect parts in red so i can have a look and see where i've gone wrong.

or better still, if someone wants to give me the answer so i can tackle chemical equilibrium segment instead :lol: j/k

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