CHEMISTRY 253

Spring, 2015 - Dixon

Homework Set 1.1 Solutions

Ungraded Problems

 

Ch. 1  Review Questions: 1, 3-10

1.  Which three gases constitute most of the Earth’s atmosphere?

 Nitrogen, oxygen and argon

3.  What is the wavelength range for visible light?

Visible light ranges from about 400 nm to 750 nm.

Does ultraviolet have shorter or longer wavelengths than visible light?

Ultraviolet has shorter wavelengths than visible light.

4.  Which atmospheric gas is primarily responsible for filtering light in the 120-220 nm region?

O2.

Which, if any, gas  absorbs most of the Sun’s rays in the 220-320 nm region?

O3.

Which absorbs primarily in the 320-400 nm region?

No major gas absorbs strongly in that region.  NO2 does absorb but is not present at high concentrations.

5.  What is the name given to finite packets of light absorbed by matter?

Photons.

6.  What are the equations relating photon energy E to light’s frequency n and wavelength l?

E = hn and E = hc/l.

7.  What is meant by the expression photochemically dissociated as applied to stratospheric O2?

Photochemically dissociated means that it is split to O atoms.

8.  Write the equation for the chemical reaction by which ozone is formed in the stratosphere.  What are the sources for the different forms of oxygen used here as reactants?

O + O2 + M → O3 + M.  O atoms originate from photolysis of O2 and O2 is a major component.

9.  Write the two reactions that, aside from the catalyzed reactions, contribute most significantly to ozone destruction in the stratosphere.

1) O3 + hn → O2 + O and 2) O3 + O → 2O2

10.  What is meant by the phrase excited state as applied to an atom or molecule?  Symbolically, how is an excited state signified?

An atom or a molecule in the excited state has a different electronic configuration than the most stable form.  It is designated with an asterisk (*).

 

Additional Problems:

1.  Rxn1.  O3 + hn → O2* + O  Rxn2. O2* + O2  → O3 + O   Net Rxn  O2 + hn → 2O

Most O created will react with O2 to form ozone.  Including that reaction, we could write the reaction as 3O2 + hn → 2O3