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Unit A
Thermochemical Changes
The Plan
• Section 11.1-Energy demands & sources.
https://sites.google.com/a/freeholdtwp.k12.nj.us/jaclynkelly/science/ener
gy-slam-poem
http://energypost.me/
Energy
• Energy is the capacity to do work.
• The direction of energy flow can be expressed as
either:
exothermic (out)
or
endothermic (in).
• Energy will flow from "hot" to "cold" until "thermal"
equilibrium is attained, that is, the substance and
environment are at the same temperature!
http://www.physicsclassroom.com/class/thermalP/Lesson-1/What-is-Heat
Photosynthesis
• Major natural contributor to stored chemical energy on
Earth.
• Takes energy from the Sun (radiant – electromagnetic
energy) & converts it into chemical energy.
Photosynthesis
• Carbon dioxide and water
react in plants in the presence
of sunlight to produce glucose
& oxygen.
• It is an endothermic reaction.
• The equation below represents the simplified process
of photosynthesis.
6 CO2(g) + 6 H2O(l) + energy → C6H12O6(aq) + 6 O2(g)
Cellular Respiration
•The chemical energy stored in the process of
photosynthesis is accessed during the process of cellular
respiration.
•In this process, glucose and oxygen react to produce
carbon dioxide, liquid water, & energy.
•It is an exothermic reaction. The equation below
represents the process of cellular respiration
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l) + energy
Hydrocarbon Combustion
•Hydrocarbon combustion is an
exothermic reaction just like cellular
respiration.
•E.g., Propane:
C3H8(g) + 5O2(g) →3CO2(g) + 4H2O(g) + energy
•Notice that in hydrocarbon combustion, water
vapor is formed, whereas in cellular respiration,
liquid water is formed. Other than that, the
equations are almost identical.
Fossil Fuels
• Biogenic hypothesis: Fossil
fuels (e.g., coal & natural
gas) had their origins in
deposits of plants & animal
matter, which got their
energy from the sun.
• Supports the claim that
fossil-fuel energy has its
origins in the solar energy
from our sun.
http://www.toonpool.com/cartoons/first%20fossil%20fuel_6415
Fossil Fuels
•Fossil fuels are a major store of chemical energy that
we use in everyday lives.
•In Alberta, ~20% of jobs are in the energy sector.
•There are four major demands for energy from fossil
fuels:
1. Heating (15%)
2. Transportation (30%)
3. Industry (40%)
4. Commercial & institutional (15%)
Some Alternative Energy Sources
•
•
•
•
•
solar heating
geothermal energy
biomass gas
hydroelectricity
nuclear power
http://www.mtu.edu/news/stories/2012/july/more-heat-more-light-steptoward-better-solar-energy-systems.html
Alternative Lifestyle
•
•
•
•
•
Improved insulation and design
Walking, biking, mass transit
Alcohol/gasohol & hydrogen fuels
Improved efficiency & waste heat recovery
Water & heat conservation
Chemical Change
• The reactant(s) have different chemical composition
than the product(s).
E.g., H2O(l)  O2(g) + H2(g)
• Some possible energy conversions:
"EXOTHERMIC"
Heat
Light
Furnace
Firefly
Energy from
Chemical Changes
Battery
Electricity
Car Engine
Mechanical Energy
"ENDOTHERMIC"
Heat
Light
Cooking
Photosynthesis
Energy Stored in
Chemicals
Electrolysis
NH3(g)
Production
Electricity
Mechanical Energy
Chemical Change
• In chemical reactions, the products have different
chemical compositions than do the reactants. Also,
the total potential energy of all the products is
different than the total potential energy of the
reactants.
• This is why energy is always either absorbed or
released in any chemical reaction.
• Exothermic reactions release energy & endothermic
reactions absorb energy
Society's major source of energy is from chemical
reactions. Examples include:
1. burning coal (carbon) and oil (hydrocarbons) to
generate steam to turn electrical generators.
2. burning gasoline/diesel (hydrocarbons) to propel
vehicles.
3. burning natural gas or heating oil (hydrocarbons)
to heat buildings and water.
4. electrochemical reactions in batteries.
5. producing, refining and shaping metals and plastics
(industry).
6. food consumption (humans, animals).
7. fertilizer production.
When is it predicted that fossil fuels in
Alberta will be depleted?
2020!
In the News
Efforts aimed at making it
easier to invest in green
energy improvements that in
the past have been
impractical or unaffordable.
New Research
Integrating solar technologies
into coal-fired power plants
could ease the transition from
fossil fuels to renewable energy
sources.
 Read p. 478 - 482
 Section 11.1 Questions
#1-8 (omit 2 & 6), 11a & 12.
Enzymes
 Read pgs. 535 – 541
 pg. 542 Section 12.3 Questions #’s 1 – 6