What is the Energy Change for the Formation of 0.39 mol of KI(s)?

[parwana]

last question

Calculate the energy change for the formation in kJ of 0.39 mol of KI(s)
given the following information: I2(s) --> I2(g) : 62.44 KJ/mol


K(s) --> K(g) : 180.4 KJ/mol


1/2 I2(g) -->I(g) : 138.05 KJ/mol


K+(g) + e- --> K(g) : -419 KJ/mol



I-(g) --> I(g) + e- : 295.16 KJ/mol

Lattice energy for KI = -649 KJ/mol


E= E(vaporization)+IE+1/2bond energy+EA+lattice energy


how would i do this, should i just add everything up?? but then what about the .39 mol??

 

[chem_tr]

First, do the necessary redox chemistry:

2K --> 2K⁺ + 2e^-
I₂ + 2e^- --> 2I^-

2K + I₂ --> 2KI

Just add the necessary numbers; but if you multiply any reaction with a number, don't forget to multiply the value with it, too.

And note that the reaction I mentioned can only become in the gaseous phase, so you'll need to use their gas-phase-transition energies given already.

About .39 moles, just multiply the value given for 1.00 moles with .39 to learn how much energy is released (or required) for this amount.

 

[parwana]

ok thanks, but can u set the numbers up, this is highly new to me

 

[chem_tr]

1) Convert solid potassium to the gaseous one (requires E₁)
2) Convert solid iodine to gaseous iodine with noticing its mole ratio (requires E₂)
3) Use these data in the redox reaction I posted in my previous thread (requires E₃; but one released and one required energies are present here)
4) Subtract the lattice energy from the total you found from 1-3 (releases E₄); it is worth noting that the 0.39 moles are to be used here.
5) Relax, as you've solved the problem

 

[parwana]

i still don't understand how u convert solid potassium to the gaseous state?? I haven't done this yet in class, but for some reason they give us h.w. in advance. Would it be too much if u could solve the problem and explain how u did it??

 

[GCT]

Gasesous state...to become their ions; how is solid K supposed to lose an electron when its bonded strongly (and thus a solid) each other?

 

[chem_tr]

Dear Parwana,

It is better for you to try to solve the problem by yourself. Please review what you have in hand; there are some energies given which will be used to bring solid potassium to the gaseous one, and ionize it; and also some for sublime iodine and ionize. Just find them and calculate the overall energy for one mol; and as you have less then one mol, multiply the value with the one you have.