Answer:
A. 1.64 J
Explanation:
First of all, we need to find how many moles correspond to 1.4 mg of mercury. We have:
where
n is the number of moles
m = 1.4 mg = 0.0014 g is the mass of mercury
Mm = 200.6 g/mol is the molar mass of mercury
Substituting, we find
Now we have to find the number of atoms contained in this sample of mercury, which is given by:
where
n is the number of moles
is the Avogadro number
Substituting,
atoms
The energy emitted by each atom (the energy of one photon) is
where
h is the Planck constant
c is the speed of light
is the wavelength
Substituting,
And so, the total energy emitted by the sample is