# Energy Unit Calorie and calorie_ by nyut545e2

VIEWS: 16 PAGES: 4

• pg 1
```									                                                                                   C + O2          CO2 + Energy

6 million
light bulbs
Thus, note that for every atom of carbon, we produce one
\$13 million of     molecule of CO2.
fluorescent
bulbs          This will turn out to be one of the major factors in the
Saving 60         increase in carbon dioxide in the atmosphere (a greenhouse
MWatts           gas).

Does this sound like a good idea?
A) Yes       B) No

Clicker Question
Each reaction with a carbon atom (in the coal for example), has       With this energy (107 Joules), approximately how many feet
an energy of 10-18 Joules.                                            can we raise a 3000 lb car? Assume 100% efficient use of
this energy.
This seems like a tiny number! But it is only one carbon atom.                                     Unit Conversions:
A) 4 feet
B) 10 feet                   1 Joule = 0.74 foot-pounds
How many atoms are there in 12 grams of carbon?                                                    1 Joule = 0.0009 Btu
C) 200 feet
D) 2300 feet                 1 Joule = 0.24 calories
Avagadro’s Number = 6 x 1023 atoms per mole
per 12 grams of carbon
Solution:
⎛ 0.74 ftlbs ⎞
A 1 pound lump of coal has about 1025 atoms of carbon. Thus                                             Energy = (10 7 J ) × ⎜            ⎟
the total energy from this chemical reaction is:                                                                             ⎝     J      ⎠
Energy = 7 ×10 6 ft − lbs
Total Energy = (Energy per Carbon Atom )× (# Carbon Atoms)

(                   )
Total Energy = 10 -18 Joules/Atom × (10 25 Atoms) = 10 7 Joules
Thus, the work that can be
done is lifting a 3000 lbs car
x 2300 feet ~ 7 x 106 ft-lbs.

Energy Unit Calorie and calorie!
Where is the energy given on this label?
calorie
New Energy Unit = Food Calorie or Calorie
Energy to change the
1 Food Calorie = 4184 Joules                                               temperature of 1 gram of water
by 1 °C

Calorie or Food Calorie (or kilo-
calorie)

Energy to change the temperature
kilo-                 1°
of 1 kilo-gram of water by 1°C

* Thus a Food Calorie is actually the same as 1000 calories
(which is the physics or chemistry term).

1
British Thermal Unit (BTU)

Energy required to change the
1°
temperature of 1 pound of water by 1°F

So really that is 1000
physics calories!

Clicker Question
Table 2.6 says that the best coal (Anthracite) which is
88% carbon, has an energy content of 13,300 Btu / lb.

So how many degrees can you raise the temperature of
260 pounds of water with the energy from one pound of
coal?
1 Jelly donut
CO2 + H2O + Energy
A)   5 degrees Fahrenheit                                         (250 Calories)
B)   50 degrees Fahrenheit
C)   250 degrees Fahrenheit
How many Joules of energy is this?
D)   3000 degrees Fahrenheit
E)   40 degrees Celsius                                                         ⎛ 1000 calories ⎞ ⎛ 4.184 Joules ⎞
250 Calories × ⎜               ⎟×⎜              ⎟   = 106 Joules !
13,300 Btu raises the temperature of 1 lbs of water by 13,300 0F                  ⎝ 1 Calorie ⎠ ⎝ 1 calorie ⎠
OR
13,300 Btu raises the temperature of 260 lbs of water by
13,300/260 = 50 0F

What if we compare this 1 million Joules from the donut, to the                      Other forms of Energy?
Potential Energy of a 60 kg object at a given height (H).

What is that height H?

PE = mgH
PE    (10 6 Joules)
H=         =
mg (60kg × 9.8m / s 2 )
PE    (106 Joules)                                Demonstration with hammering a nail into a board.
H=         =
mg (60kg × 9.8m / s 2 )                           1. Work is done by the person to give Kinetic Energy to the
hammer.
H = 1700 meters or 5000 feet                               2. The hammer then does work on the nail to give it kinetic
energy (the nail moves with some velocity).
Biological mechanism needed for efficient conversion.              3. When the nail stops moving, where did the energy go?

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New From of Energy = Heat !
Thus, when we convert energy into heat or thermal energy,
Heat was not considered a form of energy until the mid-          the kinetic energy is not seen as the net motion of a large
1800’s. Prior to that it was thought of as some type of          object (like a car or a nail), but instead as an increase in the
fluid that made things hot.                                      velocity of individual particles with random motion.

In fact heat energy (also called thermal energy) is really       Since the motion is random, the object does not appear to
just a microscopic form of kinetic energy.                       move, but just has a higher temperature.

Temperature is typically proportional to the average Kinetic
Energy of particles in a material.

Note that thermal energy can be hard to use (get at) or
convert into other forms.

Another Energy                Mass Energy                   Here is me lecturing….

Over 100 years ago, Albert Einstein                              How much energy do I have?
discovered that mass is just another
form of energy.                                                          Weight = 185 pounds

E = mc 2
Convert weight in earth’s gravity to mass         84 kg

E = mc 2 = (84kg )× (3 ×108 m / s ) 2
E = 8 ×1018 Joules !
m is mass in kilograms (SI Units) and c is the speed of
light (3 x 108 meters/second).                                   Consider that the entire USA uses 100 QBtu or 1020 Joules
each year.
Thus the energy in my body could “run all the lights” for 29
out of 365 days in a year.
What is the problem with this idea?

Clicker Question
However, in nuclear reactions, we sometimes observe that                      Fission Energy Release
there was a little more mass before compared with
afterwards.
U235 + n          Ba141 + Kr92 + 3n
U235 + n          Te139 + Zr94 + 3n
Fission Reaction (Splitting)       Fusion Reaction (Adding)
If you add the masses before and after, you find that you lost
about 3 x 10-28 kilograms in the process!
Recalling that E=mc2 (where c = 3 x 108 m/s), what is the
ratio of energy from 235 grams of Uranium (1023 atoms)
compared to that from a 1 pound lump of coal (107 Joules)?
A)   Uranium and coal energies are about equal
B)   Uranium energy is 1/100 of the coal energy
C)   Uranium energy is 1000 times the coal energy
D)   Uranium energy is 100,000 times the coal energy

E (Uranium) = mc 2 = (10 23 × (3 × 10 −28 kg ))(3 ×108 m / s) 2 ~ 1012 J

3
Nuclear fission chain reactions are
the current power source for
nuclear reactors. Isotopes of
Uranium for example are the fuel.

Nuclear weapons now utilize
both fission and fusion
reactions.
Chemical Reactions        Nuclear Reactions involve
involve atomic electrons.   proton and neutrons in the
nucleus.
Typical energy per
reaction ~ 10-18 Joules       Typical energy per                            The sun is powered by fusion
(or 10 eV)           reaction ~ 10-11 Joules                         reactions in the core. The sun will
(or 200 MeV)                                continue to “burn” for a few billion
more years before it runs out of fuel.

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