Transcript Kitchen Science - Chemistry Land Intro

Instead of high-tech rocket or
electromagnetic forces, the jets are
catapulted with the ancient power
source of steam.
Helium atom is bouncing by
using a custom motion path
set to repeat until end of slide.
So you see there is no such thing as
still air. The air molecules are
constantly moving at an average of
1,000 miles per hour.
Centuries ago it was known that the
pressure in a container could be
increased dramatically by heating
water in it.
The animation is done with
custom motion paths (line
type) to bounce balls off the
walls. “Effect Options…” was
used to set it to repeat.
The first engine was
created using water in a
heated container. An
Egyptian named Hero
invented it.
A later inventor figured he could
propel a vehicle using steam power
in the same way the Hero engine did.
A common misconception is that the
exhaust does the propelling, but how
can steam that has left the container
have any effect on the chamber?
They can’t. As the water molecules
bounce around the chamber they
strike all sides imparting a small
push (pressure) on where it strikes.
Now when the water molecule strikes
the front of the chamber it pushes the
vehicle slightly forward. Normally, it
may bounce to the back of the
chamber and cancel this effect.
However, if there is an opening then
there will be no counter push. The
vehicle received a forward push
without the backward push because
the molecules are shooting out the
nozzle without hitting back of the
chamber.
Eventually someone tried to push
a piston with the pressure of
steam. The piston was also
connected to a crankshaft to turn
up and down motion into circular
motion. Unfortunately, when the
piston reached the top, the
pressure prevented it from coming
back down.
The animation of the water vapor is done
with custom motion paths (line type) to
bounce balls off the walls.
This animation is tricky because other
objects have to move at the same time. The
“Start” setting of the objects are set to start
“With Previous”.
The top circle also spins in step with the
moving rod. The rod is the trickiest because
it moves and rotates at the same time.
A solution was to add another
chamber. With a valve the
steam can be released into a
cool chamber. The steam will
condense to liquid water. A
vacuum will be left. A vacuum
cannot pull the piston down,
but outside air pressure can
push it down.
The animation is similar to the
previous page but with a longer
sequence.
This animation is a bit complicated
so don’t expect to follow it if you
are new to PowerPoint
animations.
A more efficient design was to
create steam in a separate
chamber and then introduce the
high pressure to the piston
chamber as needed. Like
before, after the piston reaches
the top, the valve to the
condenser is opened (not shown
this time)..
Here’s are some pictures of
the steam engines used in
factories.
Here’s a portable steam
engine that could be used
around a farm.
The early steam locomotives
were so novel that they
charged people to see them
work.
Some inventors wanted the
engine to propel a vehicle that
was both a boat and an
automobile.
The steam locomotive was
one of the most evident ways
we put steam pressure to
work.
However, there was a new
way to create pressure and
that was with a combustible
liquid. It could be ignited
with a spark to produce gases
of carbon dioxide and water
vapor. This was the gasoline
engine.
Gas:
Alteration of Latin chaos space, chaos Date: 1779
The gas engine is one of the wonders of the 19th
century. Now, within three years of the 20th
century, it is a novel machine, eagerly sought by
many people. It is thought by persons who have
not studied its principles that it is a steam-engine,
using gas or gasoline as fuel for the purpose of
making steam. This is erroneous. Gas and
gasoline in specific proportion with air are
explosive material.
In the next decade the steam engine will occupy the
same relative position to the gas engine that the flint
and steel now do to the lucifer match.
the tallow dip to the electric light...
...the stage coach to the modern electric
street cars, and civilization will record another
grand stride toward the millennium.
The writer of that 1897
article knew gas
engines were much
cleaner burning than
the steam engines that
ran off of coal or
wood. However, he
didn’t realize we would
pack so many of these
gas powered
automobiles together.
The pollution again
returned.
Perhaps hydrogen in the future will be our next
jump in clean burning fuel. We may choose to let
it ignite and provide pressure like current gas
engines or generate electricity using fuel cells to
power electric motors.
9 hits
9 sec
=
1 hit
sec
0
Seconds
9
00
Hits
01
02
18
03
18 hits = 2 hits
04
½ volume
sec
9 sec
Pressure comes from the
05
The bouncing molecules are done the same way as before. This
gas molecules hitting the
time I have a digital clock going and a pressure gauge. The arrow
06
side of the container. Let’s
on the gauge is made with two arrows grouped, one is made
transparent. The spin effect makes it spin in the middle. 07
count them out loud.
So we saw that as
volume decreases the
pressure increases.
V=0.5
P=2
V=6 ,,P=5
V=0.1,
P=10
V=3, P=10
Mathematically when one
value goes down as the
other goes up, we call it
inversely proportional.
We can also show this by
having them multiply by
each other.
27 ºC = 300 K
9 hits
9 sec
=
1 hit
sec
0
Seconds
9
18
27 ºC = 300 K
We saw that we can increase pressure by reducing the
volume, but we can also do it by increasing the
temperature and therefore the speed of the gas
molecules. At room temperature the hits are 1 hit/sec
00
01
02
03
04
05
006
K
07
327 ºC = 600 K
9 hits
4.5 sec
=
2 hits
sec
327 ºC
= 600 K
0
Seconds
9
18
27 ºC = 300 K
We are going from room temperature 27
ºC = 300 K to double that temperature,
which is 600 Kelvin. Let’s count the
number of collisions at this higher speed.
We get twice the number of collisions and
therefore twice the pressure.
The faster bouncing was easy. I just
changed the speed from slow (3 sec) to
1.5 sec. There is no word for 1.5 sec.
so you set it with the Timing menu.
00
01
02
03
04
05
006
K
07
15 psi, 300 K
30 psi 600 K
3 psi
So we just saw that when temperature goes up,
so does the pressure. This makes sense because
higher temperature means the gas molecules are
going faster, colliding more often, and hitting
harder.
60 K
Pressure is proportional
to the number of gas
molecules, which we
count in moles.
Another way to increase pressure is to
increase the number of gas molecules.
This is the approach the steam engine
used by heating water.
This is also a safety problem. Any closed
container that has liquid in and gets
heated will likely increase pressure
dramatically until the container bursts.
This animation is a
copy of the previous
ones, but the sides of
the container are
separate lines that can
be flown outward at the
same time with an
simultaneous explosion
graphic (from
Autoshapes). The
sound is added with
“Effect options…”
Let’s review what we learned. If the
volume decreases the pressure will
increase. Then the reverse happens if
the volume increases. The pressure
drops as gas molecules are farther
apart.
This animation uses the
Grow/shrink emphasis
effect. It also uses the
transparency emphasis
effect. I like it because
it helps show how
pressure and volume
are related.
As we also learned, we can
increase pressure by
introducing more molecules of
the gas into the volume.
The circle is drawn and the
line type is set to be dashed
and it is set to be 6pt thick
(Draw tool bar).
The circle uses the spin
emphasis effect.
The top part of the circle is
hidden by a black box.
1.4 x 1.4 = 2
2 x 2 =2
1.5 x 1.33 = 2
doubles
We also learned that if temperature
doubles, the pressure doubles if
volume is fixed. Or if the container
is flexible, the volume will double
with pressure staying constant. Or
both can increase such that the
product of the two doubles.
• P is pressure measured in atmospheres.
• V is volume measured in Liters
• n is moles of gas present.
• R is a constant that converts the units. It's value is
0.0821 atm•L/mol•K
• T is temperature measured in Kelvin.
• Simple algebra can be used to solve for any of these
values.
• P = nRT V = nRT
n = PV
T = PV R = nT
•
V
P
RT
nR
PV
To make these quantities equal, we need a conversion
constant. We call it R (the Universal Gas Constant)
This is where I play an excerpt from the
radio program “Car Talk.” In the
recording the Car Talk experts mentioned
PV=nRT when they were explaining why
the pistons on someone’s hatchback
wasn’t working in the winter.
•
•
•
•
•
Pressure=1 atmosphere
Volume=1 Liter
n = 1 mole
R=0.0821
What is the temperature?
Let’s find what temperature the gas must be if we have the following
readings for these other properties.
Normally 1 mole of a gas at 1 atmosphere pressure takes up 22.4
liters. So it must be very cold to only have a volume of 1 liter.
Frozen carbon dioxide
(Dry Ice)
Dry ice can achieve high pressure in the
way water does when it turns into steam.
However, dry ice doesn’t not need much
heat. As it warms up more CO2 will
become gas causing a closed container to
explode.
This is a copy of the water animation. I
just changed the color of the liquid and
spheres to white.
Some people put dry ice in 2 liter bottles and
add a little water to warm the dry ice quickly.
They the put on the cap and throw the bottle out
the window. A few minutes later it explodes
with a huge boom! However, if the bottle
explodes early, this may happen…
Maybe they should have learned PV=nRT
What pressure could be reached when ¼
lb of dry ice is placed in this 2 liter bottle?
Temperature that night was 86 °F (30 °C)
Facts:
2 Liter bottle
¼ lb = 454 g ÷ 4 = 114g
PV = nRT or
P = nRT
V
CO2= 12g/mol + 2*16g/mol = 44 g/mol
114 g 1 mol = 2.6 mol
44 g
What pressure could be reached when ¼
lb of dry ice is placed in this 2 liter bottle?
Temperature that night was 86 °F (30 °C)
n
P=
R
T
2.6 mol x 0.0821 atm*L x 303 K
mol*K
2.0 L V
P = 32.3 atmospheres
32.3 atm 14.7 psi = 475 psi
1 atm
A heavy duty tire will explode around 75 psi, so we know this bottle is
going to explode at 475 psi. Remember that’s 475 pounds every square
inch. This bottle has about 50,000 lbs of total force pushing outwards.
CONVERSIONS
•
•
•
•
•
•
•
•
•
760 mm of Hg
760 torr
All
29.9 in. of Hg
Equal
1 Atmosphere
14.7 lbs. per sq. in.
Temperature conversions:
Kelvin = Celsius + 273 Evangelista Torricelli
OC = (OF -32) x 5/9
OF= OC x 9/5 + 32
Click on brown rectangles to popup an image. Image
will go away on its own. This is animation that uses a
trigger. It can make very interactive screens.
Manometers
from Greek manos meaning
sparse
sphygmomanometer
• sphygmometer
• Greek sphygmos meaning pulse (from sphyzein to
throb)
Measures to 300mm
Hg
This is the inner mechanisms of certain pressure gauges.
When a pressure cooker is used, what
causes the increased pressure?
PV=nRT
P=nRT
V
Temperature goes from 25oC to 100oC
Turn to Kelvin by adding 273 to Celsius
297K to 373K 75K/297K=25% increase in pressure
Water vapor pressure
250.000
PSI
200.000
150.000
Series1
100.000
50.000
0.000
0
100
200
Temperature Celsius
300
P1V1=n1RT1
P2V2=n2RT2
n1T1 n1T1
n2T2
P1V1= R
P2V2= R
n1T1
P1V1= P2V2
n2T2
n1T1
n2T2
n2T2
We can take advantage of the fact
that the R constant is the same even if
the conditions of the gas changes.
Change in Conditions Problem
A portable air tank holds 3 gallons of air at 90 psi. If
you took it to the river to blow up 3 inner tubes each
holding 6 gallons of air, what pressure would they
have?
90psi x 3gal= P2 x 18gal
Start
End
P1V1= P2V2
n1T1
n2T2
18gal
n1T1
15 psi
18gal
n2T2
O2
Kr
Gases are special in that no matter what the gas is,
the number of atoms (or molecules) in a set volume is
the same.
This much air weighs about
30 grams, or about the same
as 6 nickels.
The periodic table
reports the atomic mass
of all elements. For
elements that are gases,
the mass listed is what
22.4 liters (~5 gal.) of
that gas would weigh at
standard temperature
and pressure (0oC, 1 atm).
Diatomic gases are
double that weight.
N2 + O2 = 80% x 28 + 20% of 32 = 22.4 + 6.4 = 28.8 >> 1
NH3 (ammonia) 14 + 3 = 17 17/28.8 = 0.6 the density of air.
Cl2 = 35.5 + 35.5 = 71 71/28.8 = 2.49 times the density of air.
Gasoline = C8H18 > 6*12 + 1*18 = 90 90/28.8 ~ 3 times heavier
HCl (hydrogen chloride= 1 +35.5 = 36.5 36.5/28.8 = 1.27
• 520 gas cylinders (168 tons) of chlorine gas was first used as
a chemical weapon at Ypres, France in 1915. 5,000 soldiers
(about 1/3 American) died and 15,000 injured.
• The density of chlorine kept the gas close to the ground.
•
•
•
•
•
•
•
Natural gas (methane) CH4
Propane CH3CH2CH3
Acetone CH3COCH3
Carbon monoxide CO
Hydrogen cyanide HCN
Hydrogen sulfide H2S
Carbon dioxide CO2
Using the Periodic Table calculate the density of these compounds in
the vapor phase. Assume standard temperature and pressure.
In 1984 in a village in the African nation of Cameroon….
Using the Periodic Table calculate the density of these compounds in
the vapor phase. Assume standard temperature and pressure.
There is a lake known as Nyos. It’s a beautiful lake that
fills the cauldron of a ancient volcano. Nothing about
givesofclues
to the danger
that rests
its deep
On the itnight
the apocalypse,
Ephriam
Cheinwas
in hiswaters.
mud brick
house on a cliff above Nyos. Around 9 P.M., Che heard a rumbling
that sounded like a rockslide. Then a strange white mist rose from the
lake. He went to bed, feeling ill.
At first light, Che
headed downhill.
Nyos had turned a
dull red. He noticed
the silence; the
morning sounds of
songbirds and insects
were absent. He also
saw dead animals.
Frightened, he ran
farther along the lake
and downhill to the
village. There, nearly
every one of the
village's 1,000
residents was dead,
including his parents,
siblings, aunts and
uncles. It was the end
of the world, or so
Che believed.
Eye witnesses said they saw an invisible river coming down the hill knocking
down brush and small trees. It traveled at about 50 mph but could not be seen.
All told, some 1,800 people perished around Lake Nyos. Later the killer was
found to be carbon dioxide, which is not considered toxic, but its high density
keeps it close to the ground causing asphyxiation. Density also caused it to
flow down the hillsides asphyxiating more people.
Scientists found the carbon dioxide had been building up over time at the
bottom layer of the lake. Magma vents were pumping CO2 into the lake
forming carbonic acid (H2CO3) which essentially is carbonated water. The
water pressure kept it from decomposing in to CO2 gas which would float and
dissipate. However, a rock slide or small earthquake triggered the carbonic
acid to decompose into CO2 causing the lake to explode.
To prevent build up of CO2 scientists installed pipes that reach down to the
depths and trigger a release of CO2. This huge fountain is only powered by
the release of CO2.
PV=nRT
PV= g RT
Molar mass
Molar mass =
g RT
PV
An automated early warning device could be designed to pump samples
of air into a 4.0 liter container until the pressure was 3.0 atmospheres. At
that point the container is weighed and the temperature taken. Let’s say
the net weight is 21 grams and the temperature is 33OC (91OF). What
molar mass would the device calculate?
Molar mass = 21g x 0.0821 atm•L/mol•K x (273+33) K
3.0 atm x 4.0 L
Molar mass = 44 g/mole, which indicates that the air is mostly CO2, so
the alarm is sounded.
78 centimeters circumference
C=πxD
78 = 3.1415 x D
24.7 cm = D
12.35 cm = r
V= 4/3 π r3
V= 7937 cm3 ≈ 8,000 cm3
Molar mass = gRT
PV
Pressure= 30 psi
Temp 27oC
Mass of ball (empty): 600 g
Mass of ball filled: 603 g
On a lighter note, let’s solve an issue about this little people
basketball game. The basketball seems too light. Calculate what
kind of gas the basketball is filled with.