MCAT General Chemistry Question 6: Answer and Explanation

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Question: 6

6. An electron returns from an excited state to its ground state, emitting a photon at λ = 500 nm. What would be the magnitude of the energy change if one mole of these photons were emitted? (Note: h = 6.626 × 10-34 J·s)

  • A. 3.98 × 10-21 J
  • B. 3.98 × 10-19 J
  • C. 2.39 × 103 J
  • D. 2.39 × 105 J

Correct Answer: D

Explanation:

While daunting at first, the problem requires the MCAT favorite equation where h = 6.626 × 10-34 J·s (Planck's constant), is the speed of light, and λ is the wavelength of the light. This question asks for the energy of one mole of photons, so we must multiply by Avogadro's number, NA = 6.02 × 1023 mol-1.

The setup is:

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