# Homework 21 (6/1/2016)

Name: ______________________________

Section: _____________________________

Student ID#:__________________________

## Q21.1

What is the wavenumber and frequency of a 450-nm photon? How does the energy of 450-nm light compare to the energy used to overcome activation barriers in chemical reactions (i.e., thermal energy $$k_bT$$) at room temperature?

Q21.2

Convert the following absorbance of a sample to percent transmittance: (a) 0.0, (b) 0.12, and (c) 0%.

## Q21.3

An excited molecule has an average lifetime of $$2.0 \times 10^{-8} \ seconds$$, and the radiation emission is 600 nm. Find the frequency and wavelength uncertainties.

## Q21.4

What is the concentration of a lysozyme solution if a 1.0-cm wide cuvette containing the solution transmits 25% of λ = 280 nm (UV) light? The molar extinction coefficient for lysozyme at 280 nm is 26.4 L mol-1cm-1.

## Q21.5

The Doppler effect results in a shift in the wavelength of a star in astronomic meaurements, but only to a broadening of a transition in a gas; why?

## Q21.6

Which of these transitions are possible for the electronic absorption of an atom or molecule?

1. A 1s electron in hydrogen is promoted to the 2p orbital
2. A 1s electron in hydrogen is promoted to the 3d orbital
3. A 2s electron in hydrogen is promoted to the 3d orbital
4. An electron with the quantum numbers ($$n=2$$, $$l=1$$, $$m_l=1$$ and $$m_s=+1/2$$ in hydrogen is demoted (e.g., via the emission of a photon) to a wavefucntion with the quantum numbers ($$n=1$$, $$l=0$$, $$m_l=0$$ and $$m_s=+1/2$$.
5. An electron with the quantum numbers ($$n=2$$, $$l=1$$, $$m_l=1$$ and $$m_s=+1/2$$ in hydrogen is demoted (e.g., via the emission of a photon) to a wavefucntion with the quantum numbers ($$n=1$$, $$l=0$$, $$m_l=0$$ and $$m_s=+1/2$$.