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# Bond enthalpies mk 2 watch

1. How do i do question 3?

EricPiphany samb1234 Kvothe the arcane
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2. 2.1 Exercise 2 - Bond dissocation enthalpies.doc (33.5 KB, 83 views)
3. bump
4. (Original post by thefatone)
How do i do question 3?

EricPiphany samb1234 Kvothe the arcane
Draw a hess cycle
5. (Original post by samb1234)
Draw a hess cycle
how would i do that?
6. (Original post by thefatone)
how would i do that?
Well you want to know the average dissociation energy of a c-cl bond, so essentially you are trying to find ccl4 -> C + 4 Cl. Think about what data you have that could help you achieve that
7. (Original post by samb1234)
Well you want to know the average dissociation energy of a c-cl bond, so essentially you are trying to find ccl4 -> C + 4 Cl. Think about what data you have that could help you achieve that
so far i've put C+2Cl2--->CCl4 and i've but C+Cl2 below it and 2 arrows going from C+Cl2, 1 to C+2Cl2 and 1 to CCl4 have i done it right?
8. (Original post by thefatone)
so far i've put C+2Cl2--->CCl4 and i've but C+Cl2 below it and 2 arrows going from C+Cl2, 1 to C+2Cl2 and 1 to CCl4 have i done it right?
9. (Original post by samb1234)
oh? so if it's combustion then the arrow go down but formation goes up?
also why do both arrows go down? talk me through pls
10. (Original post by thefatone)
oh? so if it's combustion then the arrow go down but formation goes up?
also why do both arrows go down? talk me through pls
The bond dissociation enthalpy is the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state. So therefore we need the arrow from CCl4 to be downwards, and we are given the values for C(s) to gas and Cl2 ->2Cl in the question
11. (Original post by samb1234)
The bond dissociation enthalpy is the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state. So therefore we need the arrow from CCl4 to be downwards, and we are given the values for C(s) to gas and Cl2 ->2Cl in the question
so why does the arrow on the left go down aswell? Since C+2Cl2 to C+Cl2 are both separate atoms right? so what bond are we breaking here to give separated atoms?
12. (Original post by thefatone)
so why does the arrow on the left go down aswell? Since C+2Cl2 to C+Cl2 are both separate atoms right? so what bond are we breaking here to give separated atoms?
Well technically you should have more than one arrow going down. One for the Cl2 ->2Cl (we need 4 Cl so you need two times the value given in the question) and one for C(s) -> C(g) I just did them as one to simplify
13. (Original post by samb1234)
Well technically you should have more than one arrow going down. One for the Cl2 ->2Cl (we need 4 Cl so you need two times the value given in the question) and one for C(s) -> C(g) I just did them as one to simplify
^^ thanks so much for your help i managed to catch someone and they explained everything to me so basically i learnt hess's law and how to work stuff out in about 40 mins o.o

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