[theanonymous]

Problem 1


So Part A would be...

CH₃-H + Cl-Cl  CH₃-Cl + H-Cl

∆H_reaction = (enthalpy of bonds broken) - (enthalpy of bonds formed)
∆H_reaction = (439 + 243) - (351 + 432)
∆H_reaction = 682 - 783
∆H_reaction = -101


QUESTION 1: Is that right?

And Part B would be...

CH₃-H + F-F  CH₃-F + H-F

∆H_reaction = (enthalpy of bonds broken) - (enthalpy of bonds formed)
∆H_reaction = (439 + 159) - (459 + 571)
∆H_reaction = 598 - 1030
∆H_reaction = -432


Table 4.3:


Problem 2


QUESTION 2: This is what I did. Does it look right?



QUESTION 3: I understand the initiation and the propogation steps, but what happens in the termination step??? Is it just the combination of the radicals?

[theanonymous]

I also need help with Problems 3, 4, and 5! I already did it but I need someone to kind of verify my work and answer some of the questions I have

Problem 3



QUESTION 4: Does this look right? But isn't the graph supposed to look exothermic?



Problem 4



What I did:



Problem 5



QUESTION 5: I copied down the Hammond Postulate concept from my notes and used it to answer the question. Am I right?

[theanonymous]

 
Anyone???

[discodermolide]

I think you need to break this down into smaller units. For me there is too much info. to read.

[theanonymous]

I think you need to break this down into smaller units. For me there is too much info. to read.

Well I already did all of the work - I just need someone to kind of tell me whether or not what i've done so far is right. But you can ignore problems 1 and 2 because I'm pretty sure I got those right.
The ones I really need help on are Problems 3, 4 and 5. They all relate to each other.

[theanonymous]

Oh great...this is depressing.

[NL-bucky]

For problem 2:

Please keep in mind that whole arrows represents the movement of 2 electrons, for the movement of 1 electron you use half-arrows.

For your calculated energies: you do not only break a bond in each propagation step, but also form one. Re-assess this calculation.

For the diagrams: make sure you use the correct energies for the right steps (i.e. only the propagation steps!) - Question 4 is answered with this remark I reckon.

For 5: What feature of the energy diagram do you use to assess the reaction rate?

[discodermolide]

What is depressing?

[NL-bucky]

I'd say you did pretty well already!

[theanonymous]

For problem 2:

Please keep in mind that whole arrows represents the movement of 2 electrons, for the movement of 1 electron you use half-arrows.

For your calculated energies: you do not only break a bond in each propagation step, but also form one. Re-assess this calculation.

For the diagrams: make sure you use the correct energies for the right steps (i.e. only the propagation steps!) - Question 4 is answered with this remark I reckon.

For 5: What feature of the energy diagram do you use to assess the reaction rate?

Ok so you're saying my answers to Problem 1 is right? However, my answer to Problem 2 (the calculated energies) should be the same as Problem 1???

I'm confused

[NL-bucky]

Problem 1 is asking for the energies of the overall reaction, which I believe you calculated correctly. Problem 2 is asking for the energies of the individual propagation steps, so that should neither be the same as problem 1, nor should be only the energy of the bonds broken (which you calculated I believe). But you should calculate the answer for 2 in a similar manner as the answer for problem 1, just with different numbers.

[theanonymous]

Ok, so according to Table 4.3,

The corresponding ΔH for each propogation step would be...

Propogation A

Energy cost to BREAK CH₃-H bond is ΔH = +439 kJ/mol
Energy cost to FORM H-Cl bond is ΔH = +432 kJ/mol

Do I add this up or leave it like this?

Propogation B

Energy cost to BREAK Cl-Cl bond is ΔH = +243 kJ/mol
Energy cost to FORM CH₃-Cl bond is ΔH = +351 kJ/mol

Do I add this up or leave it like this?

[NL-bucky]

Add them up...

[theanonymous]

So

Propogation A: ΔH = +871 kJ/mol
Propogation B: ΔH = +594 kJ/mol

Awesome!

So for the diagrams, you said to use the correct energies for the right steps (i.e. only the propagation steps)...

so would I be using the values from Propogation A for the first diagram? ΔH = +439 kJ/mol and ΔH = +432 kJ/mol? It would look like a (kind of balanced) bell shaped curve right?

[theanonymous]

Because my teacher just wants the potential energy diagram for the FIRST propagation step of the radical chlorination of CH4