Standard enthalpy change for iron oxidation in hand warmer

[biochem850]

Homework Statement

Chemical hand warmers produce heat when they're removed form their airtight plastic wrappers. These hand warmers utilize the oxidation of iron to form iron oxide. Calculate standard change of enthalpy for reaction and compute how much heat is produced from a warmer containing 15.0g Fe?

Homework Equations

Summation notation involving products and reactants to calculate standard enthalpy of change

The Attempt at a Solution

[2(-824.2kj/mol)]-[4(0)+3(0)]= -16484.4kJ/mol iron oxide

I used the stochiometric relationships of the equation of iron+oxygen---> iron oxide to convert grams to moles of iron to moles of iron oxide and used the predetermined standard change of enthalpy and I got -221kJ emitted but the correct answer is -111kJ emitted.

 

[Borek]

[2(-824.2kj/mol)]-[4(0)+3(0)]= -16484.4kJ/mol iron oxide

Bolding mine. This is a correct stoichiometric coefficient, but you can't use 2 moles and claim the result is per one mole.

And it is 1648.4 kJ, not 16484.4kJ, but that's probably just a typo.

 

[biochem850]

Bolding mine. This is a correct stoichiometric coefficient, but you can't use 2 moles and claim the result is per one mole.

And it is 1648.4 kJ, not 16484.4kJ, but that's probably just a typo.

Please forgive me (I'm usually quite good with chemistry but I've been reviewing thermochemistry all day). If I'm understanding what your saying, you would change the conversion factor from 1648.4 kJ/mole to 1648.4 kJ/2 mole iron oxide and use this relationship to convert from 15.0g Fe to moles of Fe to moles of iron oxide and then employ the determined relationship.

I've arrived at the correct answer but I want to be sure my logic is sound (I'm almost done reviewing thermochemistry and I want to move on to the Quantum mechanical model of atoms).

Thanks for your help!

 

[Borek]

If I'm understanding what your saying, you would change the conversion factor from 1648.4 kJ/mole to 1648.4 kJ/2 mole iron oxide and use this relationship to convert from 15.0g Fe to moles of Fe to moles of iron oxide and then employ the determined relationship.

And you are understanding correctly.