Electronvolt to joule/mole

1. Jul 28, 2015

omidd

Dear Friends,

Could you tell me how I can convert electronvolt to joule/mole for silicon material? I want to convert 4530 ev to joule/mole for silicon.

2. Jul 28, 2015

NaOH

The trick I like to use is to "substitute" the units.

Recall that 1.6*10^-19 J = 1 eV

We can write 6.7 eV as 6.7 * 1eV. Substitute the 1eV from earlier and you get 6.7*1.6*10^-19 J.

I'll leave the rest as an exercise, but if you get stuck, try thinking for how much silicon the 4530eV is for.

3. Jul 28, 2015

omidd

I calculated it. Is that correct?

number of atoms = 27000
silicon mass = 28.0855*1.66054*10^-27 Kg
1 Kg silicon = 35.6 mole

(4530*1.6*10^-19)/(27000*28.0855*1.66054*10^-27 ) = 600 KJ/Kg

600/35.6 = 16.85 KJ/mole

4. Jul 28, 2015

NaOH

I have a few questions:

1) What is the energy of 4530eV for? Is it for some atomic transition?

2) Where did the number of 27000 atoms come from? Is the 4530eV for 27000 silicon atoms?

5. Jul 28, 2015

omidd

1) That is enthalpy when the solid melts.
2) 4530 ev is for 27000 atoms.

6. Jul 28, 2015

NaOH

Yes, your calculation seems correct, but a few things to consider:

1) You might want to check the math again. I obtained 16.168 kJ/mol. The discrepancy might be because you approximated the value to be 600J/kg.

2) From wikipedia, we have:
So, if this is one way to convert if you have good memory!

3) While your calculation is correct, I find it rather long. In fact, if you notice, 1/(35.6(mol/kg)*28.0855*1.66054*10^-27(kg))=6.023078*10^23 /mol, which is the Avogadro constant!

4) In view of point 3, in fact, you can directly compute using (check units by cancelling them like in fractions):
4530eV/270000atoms * 1.6*10^-19 (J/eV)* 6.022*10^23 (atoms/mol) = 16.168kJ/mol.
Indeed, 1.6*10^-19*6.022*10^23 = 96352 J/mol, which converts 1.04*10^-2eV to 1kJ/ mol in point 1!