Page 147 - Basic physical chemistry for the atmospheric sciences

Oxidation-reduction reactions l . l\

a sulfurous acid, H S0 (aq), solution that i s a strong
3
2
reductant. The sulfurous acid solution is oxidized to a
sulfuric acid, H S04(aq), solution. Which gase , ab­
s
2
sorbed into cloud drops from the atmosphere, do you
think may be involved in this oxidation?
(d) During the day the concentration of C02 in forests is
about 305 ppm, but during the night it is about 340 ppm.
(e) The energy provided by burning fossil fuels (coal, oil,
wood, etc. ) derives from the sun.
(f) The burning of fossil fuels generally increases the C02
content of the atmosphere but the burning of recently
grown trees does not.
(g) The surface of the Earth i s a redox boundary between
the planet's reduced metallic core and an oxidizing at­
mosphere.
(h) The tendency of most materials to be oxidized by air is
counteracted by photosynthesis .
(i) Much chemical technology depends n the reduction of
o
materials to lower oxidation states (e.g. , H and N H 3),
which are then reoxidized when used.
(j) If the values of x electrode potentials are known, it
i s possible to determine the spontaneous directions of
x(x - 1 ) /2 chemical reactions under standard conditions.
(k) A chemical reaction in an aqueous solution that has a
negative value of E.!en can be driven in the forward
direction by applying an electric potential difference
that exceeds IE.!eul in an appropriate direction. (This is
i
the basis of electrolys s . )
t
(I) A voltmeter attached o the circuit f a n electrochemi­
o
cal cell serves as a "Gibbs free-energy meter."
(m) Stronger oxidants than oxygen do not persist for long
in natural environments.
(n) Equal numbers of gram-equivalents of two substances
react exactly with each other.
6. 1 2 . Write down the half-reactions fo r the following oxidation­
reduction reactions . In each case, indicate which is the oxi­
dation half-reaction and which the reduction half-reaction,
and which species s the oxidant and which the reductant.
i
2
3
2
(a) Fe + (aq) + Cu + (aq)- Fe + (aq) + Cu + (aq)
z
(b) Zn(s) + 2H + (aq) - Zn + (aq) + H 2 (g)