GROUP EXERCISE NUMBER TWO                   CHM 1045 -- Dr. Light


Energy Consumption and the Greenhouse Effect.  What's All the Fuss
About?

You have all read public press accounts of the Greenhouse Effect,
i.e.  gases like carbon dioxide in the air trapping infrared
radiation and  causing the earth to heat up.  (See a brief
discussion on page 94 of your text, and also the newspaper article
on the Prentice Hall web page for chapter 3).  It is clear that
carbon dioxide concentration is increasing.  Scientists disagree on
how much of an effect this change will have on  global warming, and
that debate centers on issues beyond the scope of this  course (and
involves massive computer models of global temperature change).

However it is not beyond the scope of this course to calculate the
effect  each of us has on the annual production of carbon dioxide,
and this exercise asks you to do just that for an average family of
four  persons in the United States:

(a)  Calculate how much CO2 is produced by breathing.
(b)  Calculate how much CO2 is produced by driving a car.
(c)  Calculate how much CO2 is produced to generate the electricity 
     the family uses.
(d)  Compare these figures with that you would obtain if you used 
     the value given in your text on page 172 (i.e., the average  
     person consumes 1.0 x 10^6 kJ of energy per day) and assumed 
     all this energy came from combustion of natural gas.
(e)  Based on your figures from (d), how many people would it take 
     to increase the CO2 in the atmosphere by 0.1 part per million 
     over a 10 year period? 

As before, some assumptions will need to be made, and following are
suggestions to get you started.

Part a

You can calculate from the equations on page 170 of your text that
burning carbohydrate produces 2.1 mmoles of CO2 per kJ of heat
produced, and that  burning fat produces 1.5 mmoles of CO2 per kJ
of heat produced.  (Can you see where I get these numbers?)

Assume an average diet produces 1.8 mmol CO2 per kJ consumed.
Assume an average person consumes a diet of 10,000 kJ per day. 
(This corresponds to 2390 Cal) 

Part b

Assume that the family of four drives 15,000 miles per year in a
car that  gets 20 miles per gallon.  Assuming the gasoline is
isooctane (C8H18),  calculate the grams of CO2 produced in a year
by the car if all the isooctane is converted to CO2.  The density
of octane (C8H18) is 0.7025 g/mL.  (You could have looked this up).


Part c

Assume that the family of four consumes 1200 kilowatt-hours of
energy per  month on average over the year, which would cover
heating, cooling, and  other electrical uses.  Further assume that
this energy is generated by a  power plant that burns natural gas,
and that the efficiency of production  of the electrical current is
20%  (i.e., only 20% of the heat energy from  burning natural gas
ends up as electrical energy).  Natural gas is  primarily methane
(CH4), and an equation for energy from combustion of  methane is
given on page 150 (using the value for gaseous water as a 
product).  Calculate how many grams of CO2 will be produced in
burning  sufficient methane to produce the annual electrical energy
needs of this  family.  (1 watt of electrical energy = 1 J per
second.  In other words, 1 J of energy is 1 watt-sec.  Conversion
of kilowatt-hours to J is explained on page 754 of your text).

Part d.

Finally, sum up these values.  Then compare the sum with the energy 
consumption figure given on page 158 (1.0 x 10^6 kJ per day per
person),  where you can assume all of the 1.0 x 10^6 kJ consumption
is in the form of  combustion of methane (including the 80% energy
loss in converting the heat energy to electrical energy).  

Part e.

Use the value of 1.0 x 10^22 Liters for the volume of the
atmosphere as obtained in group problem number 1, and an average
density of 0.022 moles of air molecules per liter.  Parts per
million refers to one CO2 molecule per million air molecules.


This exercise is due at the end of class on Monday, March 1.  You
may choose to divide up the calculations among members of your
group, but everyone should check the work before it is turned in.

Dr. Light

PS.  Please try to make your paper legible, and don't forget to
staple the pages together, and sign your name so that I can read
it.