Chemical Questions
Some were chosen for their
timeliness; why?
Organ Pipe Deterioration (p. 113)
• Observation: The pipes of some 19th
century organs of N. Europe deteriorated.
• Analysis: These pipes were made of tin.
– At T > 55F or 13 oC, white tin or β-tin is most
stable. It is solid, shiny, dense, has a bodycentered tetragonal unit cell.
– At T < 55F or 13 oC, grey tin or α-tin is most
stable. It is powdery, loose, has a cubic unit
cell.
β-Sn to α-Sn
• β-Sn and α-Sn are two different allotropes
or forms of tin (like O2 and O3 or graphite
and diamond).
• As temperature decreases, β-Sn  α-Sn
spontaneously and auto-catalytically (i.e. it
speeds up once it starts).
• The organ at New College (Oxford U)
http://www.newcollegechoir.co.uk/organ.ht
m
Lime and Acid Rain (p.46)
• Acid rain is a product of water and coalfired power plant emissions
– SO2(g) + H2O (ℓ) + ½ O2 (g)  H2SO4
– This acid ends up in the atmosphere but
precipitates as rain and snow.
– NO and NO2 + water produce nitric acid
– Unpolluted rain has pH of 5.2; acid rain pH
can be as low as 2.4.
Prevention of Sulfuric Acid
Formation
• Strategies to prevent SO2 from being released
into atmosphere are many and varied.
+ CaO(s, lime)  CaSO3(s)
+ CaCO3(s, limestone)  CaSO3(s) + CO2(g)
+ Ca(OH)2(s, slaked lime)  CaSO3(s) + H2O
+ NaOH(aq) + 1/2 O2  Na2SO4(s) + H2O
+ Na2SO3 + 1/2 O2  2HSO3-(aq)
+ zeolites  chemisorption (chemical) or adsorption
(physical)
• Recover S as appropriate.
Leavening Agents (p 67)
Puff Pastry, Bread, Yeast…
• What causes puff pastry to “puff” up, bread
and cakes to rise?
• A gas is produced throughout the dough
via various mechanisms.
• As the item is baked, the volume of the
gas increases with temperature (whose
law?) and the dough rises and then the
gas bubbles are baked into the dessert.
Liquid vs Vapor Volume
• 18 mL liquid water expands to
– 24 L = 24,000mL of gas at STP
– 30 L gas at 100 oC or 212F
– 42 L gas at 200 oC or 400F.
What Produces the Gas Molecules
• Mixing or beating a cake mix with eggs, oil
and water incorporates air bubbles into the
batter.
• Yeast added to bread ferments the sugar
(composition and compound type?) in the
dough producing CO2 gas and water.
• Steam leavening occurs when water in the
puff pastry vaporizes.
One More Mechanism
• Baking soda or NaHCO3 + H+(aq) 
Na+ (aq) + H2O(g) + CO2(g)
Source of acid?
Thermochemistry
• “Thermo”: Heat or energy associated with
• “Chemistry”: Chemical reactions
• Thermochemistry asks is heat given off by
a reaction or is heat required for the
reaction to proceed? In either case, how
much heat?
• The chemical industry is concerned with
the cost of heat needed and also how to
recycle heat given off.
Exothermic Reactions
• Some reactions give off heat when R  P
– R  P + heat
– We observe the reaction container getting hot
or heat being generated by the rxn.
– Chemical Examples: burning of fuel, hot
packs
– Phase (Physical) Changes: condensation
from gas to liquid or liquid to solid.
Endothermic Reactions
• Other reactions absorb heat when R  P
– R + heat  P
– We observe this type of rxn by the container
getting colder as the heat from the container
is absorbed or we have to provide heat
– Chemical Examples: cold packs (p 134),
– Phase (Physical) Change: evaporating a
liquid to a gas or melting a solid to a liquid.
Spraying Orange Orchards to
Prevent Their Freezing (p. 107)
• When temperatures drop below freezing,
citrus fruits are especially vulnerable to
freezing (water content freezes).
• Strategies to prevent this:
– Use heaters to heat orchard air.
– Spray warm water on tree trunks; as water
cools, heat is released to heat orchard air.
– Spray water on fruit if T < 0 oC so liquid water
freezes (exothermic). Also ice insulates.
Why Does a Setting Cast get
Warm? (p. 133)
• Plaster of Paris (like flour) + water 
Gypsum (hard solid cast)
• CaSO4•½ H2O(s) + 3/2 H2O(ℓ) 
CaSO4 •2H2O(s)
• Exothermic or Endothermic?
• Calculation says that the temp will
increase from 25 oC to 117 oC!
Making Snow on Spirit Mountain
(p. 131)
• A snow making machine spews water vapor and
compressed air through a nozzle.
• The water vapor expands as it passes through
the nozzle and then freezes to a solid or snow.
• Recall that when we heat a gas at constant T, its
volume increases (expansion). We have to
provide heat in this case.
• If we insulate the gas from the heat source but
still allow the gas to expand, another energy
source has to be found to expand the gas.
Snow Making
• Now recall that molecules are always in motion
(KMT) and the higher the temp, the faster they
move and the more energy they have.
• So if we cool the molecules, they will lose
energy. This is the energy used to expand the
water vapor. So as the water vapor passes
through the nozzle, its temp drops as it expands.
And the temp drop is sufficient to cause the
formation of snow.
Northern Lights (p. 145)
• Solar flares create fast moving ions and
electrons.
• These enter our atm and ionize and/or
excite and/or dissociate oxygen, nitrogen,
etc. Ie non-ground states are created.
• When the ion regains its electron and/or
de-excites and/or associates (return to
ground state), light is emitted.
Colors of the Aurora Borealis
• O2+ + e-  O2 λ = 630 nm red
• 2O  O2
λ = 557.3 nm green-yellow
and λ = 630 nm red
• N2+ + e-  N2 λ = 391.4 - 470 nm violet,
blue