A lithium flame has a characteristic red color due to emissions of wavelength 671 nm. What is the mass equivalence of 1 mol of photons of this wavelength (1 J = 1 kg·m²/s²)?

Respuesta :

Answer:

1.98x10⁻¹² kg

Explanation:

The energy of a photon is given by:

  • E= hc/λ

h is Planck's constant, 6.626x10⁻³⁴ J·s

c is the speed of light, 3x10⁸ m/s

and λ is the wavelenght, 671 nm (or 6.71x10⁻⁷m)

  • E = 6.626x10⁻³⁴ J·s * 3x10⁸ m/s ÷ 6.71x10⁻⁷m = 2.96x10⁻¹⁹ J

Now we multiply that value by Avogadro's number, to calculate the energy of 1 mol of such protons:

  • 1 mol =  6.023x10²³ photons
  • 2.96x10⁻¹⁹ J *  6.023x10²³ = 1.78x10⁵ J

Finally we calculate the mass equivalence using the equation:

  • E=m*c²
  • m=E/c²
  • m =  1.78x10⁵ J / (3x10⁸ m/s)² = 1.98x10⁻¹² kg

Lanuel

The mass equivalence of 1 mole of photons of this wavelength is equal to [tex]1.78 \times 10^{-11} \;kg[/tex]

Given the following data:

  • Wavelength = 671 nm = [tex]6.71 \times 10^{11}[/tex] m.

We know that the speed of light is [tex]3 \times 10^8[/tex] m/s.

Planck constant = [tex]6.626 \times 10^{-34}\;J.s[/tex]

Avogadro constant = [tex]6.02 \times 10^{23}[/tex]

To determine the mass equivalence of 1 mole of photons of this wavelength:

First of all, we would calculate the energy associated with the photons of this wavelength by using the Planck-Einstein relation:

Mathematically, Planck-Einstein relation for photon energy is given by the formula:

[tex]E = hf = h\frac{v}{\lambda}[/tex]

Where:

  • E is the maximum kinetic energy.
  • h is Planck constant.
  • f is photon frequency.
  • [tex]\lambda[/tex] is the wavelength.
  • v is the speed of light.

Substituting the parameters into the formula, we have;

[tex]E = \frac{6.626 \times 10^{-34} \; \times \;3 \times 10^8 }{6.71 \times 10^{-7}} \\\\E = \frac{1.99 \times 10^{-25}}{6.71 \times 10^{-7}} \\\\E=2.96 \times 10^{-19} \;Joules[/tex]

For the energy of 1 mole of photons:

[tex]E = 2.96 \times 10^{-19} \times 6.02 \times 10^{23}\\\\E = 1.78 \times 10^5 \; Joules[/tex]

Now, we can find the mass equivalence of 1 mole of photons by using the formula:

[tex]E = mc^2\\\\m = \frac{E}{c^2} \\\\m = \frac{1.78 \times 10^5}{(3.0 \times 10^8)^2} \\\\m = \frac{1.78 \times 10^5}{(9.0 \times 10^{16})}\\\\m = 1.78 \times 10^{-11} \;kg[/tex]

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