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Pressure and Gases

This prezi was made for a high school chemistry class for a unit of study on pressure and gases. In this prezi, you will learn about pressure and its effect on temperature and volume of gases.
by

Valerie Henderson

on 5 April 2016

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Transcript of Pressure and Gases

5
Unit: Pressure and Gases
Direct and Inverse Proportions
Pressure Demos
If a chicken and a half can lay an egg and a half in a day and a half, how long does it take a chicken to lay an egg?

Hawai'i` minimum wage is $8.50/hr.
Make a plot of salary vs. hours worked.
Connect the points.
What do you see?
A line with a slope of 8.50 that goes through the origin
a direct relationship.
Many jobs pay based on a salary. What is a salary?

Direct proportions = linear relationship
Not all linear relationships are direct proportions
If 5 cats can catch 5 mice in 5 days,
how many days does it take 3 cats to catch 3 mice?

On whiteboard:
cats
mice
days
5
5
5
How many mice can 5 cats catch in 1 day if they can catch 5 in 5 days?
5
1
1
3
How much less time do you have?
1/5 of the time
so they can catch 1/5 the mice
1
1
Now, if 5 cats catch 1 mouse in 1 day, how many days does it take one cat to catch 1 mouse?
if you have less cats, it takes more time to catch the mice.
5
This is an inverse proportion
How many less cats do you have?
1/5 less cats
So how much more time does it take to do the mice catching?
5x more time
5
Let's look at how we were able to solve this problem...
If a teen and a half can mow a lawn and a half in a day and half, how many days will it take 5 teens to mow 20 lawns?
So what do we see in this cat problem with the 3 variables?
2 direct relationships and 1 inverse relationship
Only true if we hold 1 variable?
CONSTANT
Now, give me a rule for an equation with only multiplication AND NO DIVISION...How can you easily tell whether or not variables are inversely or directly related?
If they're on the same side, inversely related.
If they're on different sides, directly related.
Let's look at this with numbers...
cd = 5m
If we hold m constant, what do we have on the right side?
A new constant.
What's the relationship between c and d?
inverse
If you increase c, then what has to happen to d?
decreases
How?
proportionally
So if we make c 5 times bigger
What do we have to do to d?

Make-shift lid for a cup of water
Materials: Cup full of water
Index Card big enough to cover cup.
What will happen when I tip the cup upside down?
When I tip the cup upside down, the index card stays attached and no water spills out of the cup.
Why?
The pressure applied to the index card by the water is less than the pressure of air outside the cup.
There is less pressure on the card by the water than the pressure exerted by the outside air.
Water Barometer
AKA: Goethe Barometer after the German mathematician who came up with the weather ball thermometer using Toricelli's ideas.
materials: graduated cylinder full of water.
Pan full of water
What will happen when I fill the cylinder w/ water and invert it in the pan of water?
The water will stay in the graduated cylinder
What will happen if I put it in the vacuum pump?
Why?
As the pressure is decreased inside the bell jar, the the height of water in the cylinder will fall.
What happens as I slowly let the air back into the bell jar?
As the pressure inside the bell jar is increased, the column of water in the cylinder will rise.
Why do we use mercury in thermometers instead of water?
Mercury (Hg) is more dense than water. Also, water freezes at 0 C. (Hg doesn't freeze until -38.83 C
Since water is less dense, it would require a very tall column which would be unreasonably tall.
Pb floats in Hg!
Here's a very simple water barometer.
Pretty low budget set up
standard atmosphere = 1 atm
1 atm = 101325 Pa = 101.35 kPa
101.35 kPa = 760 mmHg
760 mmHg = 760 torr
atm = standard atmosphere
Pa = Pascals
kPa = kilopascals
The torr (symbol: Torr) is a traditional unit of pressure, now defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 101325/760 ≈ 133.3 pascals.

Historically, one torr was intended to be the same as one "millimeter of mercury". However, subsequent redefinitions of the two units made them slightly different (by less than 0.000015%). The torr is not part of the International System of Units (SI), but it is often combined with the metric prefix milli to name one millitorr (mTorr) or 0.001 Torr.

The unit was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.[1]
Balloon vs Marshallow
Materials: balloon
marshmallow
vacuum pump
bell jar
What do you think will happen to the balloon in a vacuum?
What do you think will happen to the marshmallow in a vacuum?
As I turn on the vacuum and decrease the pressure inside the bell jar...the balloon inflates and the marshallow shrivels.
But why, you ask?
Let's start with the balloon:
The balloon inflates because the decreased pressure allows for the gas to increase in volume.
So we decreased pressure and volume increased.
Is that an inverse or direct relationship?
inverse because as pressure decreases, volume increases.
What happens when I evacuate the vacuum, increasing the pressure?
As pressure increases, volume decreases
Now for the mallow:
As you decrease the pressure, why doesn't the marshmallow expand?
When pressure is decreased, air outside the bubbles pushes less than the air on the inside. The higher pressure on inside the mallow is able to push the walls of the air bubbles out.
What's making the balloon expand?
Why does the air in the balloon make it expand when normally it won't do that on it's own?
Boyle's Law Lab
In this unit, we will be studying the relationships between these 4 variables in terms of gases:
Pressure
Temperature
# of particles
volume
In this lab, you will use our learning for day 1 and 2 of this unit in order to experimentally gather data in order to analyze and determine the type of relationship between pressure and volume. How do they vary related to one another? Is this a direct or inverse relationship?
Don't answer those ? now...those are questions for the lab experiment
Quiz Correction Time - T&G
You're going to be experimenting with syringes
So I can seal the end of the syringe and press the plunger in.
I can compress this air.
What happens when I try with water?
Nope, can't do it.
Why?
Gas particles are farther apart from each other (there's large empty space)...
solids/liquids - particles are closer together. No space to compress them
a) pressure
b) volume
c) temperature
d) # of particles
kPa
L
K
mol
kiloPascals
Liters
Kelvin
mole
abbrv.
full name
If you crush the container, without letting the air out, what happens to the pressure inside the container?
increases
Now, everyone will get a syringe...
Rules: Never pull out the plunger all the way! It weakens the integrity of the rubber seal and then the syringe doesn't work any more.
When you push in the plunger, what happens to the air?
it comes out
When you pull out the plunger, what happens to the air?
air goes in
But you probably already knew that...
So, we're going to go futher...why?
shhh...
Think on that for a bit. Don't say it yet.
Art Time!
Set your plunger to 20 mL
Now, set your plunger to (without removing your finger!) 10mL
Place your finger over the opening of the plunger, don't remove it.
Finally, keeping your finger on the opening, set the plunger to 40mL.
Now, draw those 3 situations. Be prepared to be called upon to draw your representation on board.
When drawing the 10mL represenation, draw yours based on the 20mL representation.
Why do the circles have arrows?
They're moving...fast like
Why are there the same number of circles?
You capped the syringe. Particle number doesn't change because you sealed the opening. They couldn't escape.
Ok, back to the syringe...
Set your plunger at 20mL. Plug the opening. Push in the plunger to 10mL. Let go. What happens?
The plunger returns to 20mL or relatively close to it.
You explain why?
What did we do when we changed the volume from 20mL to 10mL? What happened to the particles inside?
The collision frequency of the gas particles with the walls of the container changed.
The number of collisions increased when the volume decreased.
This is what gas pressure comes from.
Now, why did the plunger not go past 20mL?
Now, in our lab, we want to analyze the relationship between pressure and volume...
What must we keep constant?
Temperature
# of particles
How?
Well, the temperature in the room is going to stay the same.
How?
Cap end of syringe.
Lab Set up
2 laptops
lab instructions - on my website next to today's breakdown.
syringe connected to a gas pressure sensor connected to a lab pro that is connected to one of the computers.
Feb 6
Unit 9
Day 3
Why did the stopper of your syringe stop at 20mL and not go past it?
Well...
It stopped at 20 mL because the pressure outside was equal to the pressure inside.
Think. Partners. Sticks.
What is the pressure outside the syringe?
air pressure
Which is equal to?
about 1 atm. Storm today so air pressure a bit lower but still very close.
When you decreased the volume from 20mL to 10mL, the pressure inside became greater than the pressure on the outside
equilibrium
Day 5 - Feb 10
Gay Lussac's Law Lab

1. Turn in corrected ChemQuests
2. Get out outline (turn to part III)
3. Quiz 9.3
4. Boyle's Law Lab Processing
5. Gas Law Summary Chart
6. To the Lab!

The Kelvin Temperature Scale
Today, we're going to talk a little bit about why we need a new temperature scale (Kelvin) and why Celsius won't work for gases.
Celsius vs Kelvin?
relative
absolute
A
change of
1 degree C is equal to 1 K
compare:
based on mp and bp of pure water
O degree C = freezing point of water
@ 1 atm
100 degree C = boiling point water
based on absolute zero
How do we convert between the two?
degree C = K - 273
K = degree C + 273
Which is bigger?
K
No negative temps in K
Upper limit to temp?
No
Lower limit?
Yes
Boyle's Law Lab Processing:
Last class, in our lab, we looked @ the relationship between P and V
If P and V are inversely related...Which would you expect your equation to be?
PV = K
or
P = K
V
Vote: 1 or 2 on your fingers
1.
2.
Remembering from Day 1...Is this more similar to 1. salaries or 2. rectangle area?
vote. fingers.
Rectangle area. When we kept area the same, as length increased, width decreased. How?
proportionally!
(I'm bringing it back!)
However, this constant is not really very useful...Why?
Think. partners. sticks
Well...what does the constant depend on?
ie. What did we have to keep constant in our lab?
temperature and # of particles
Really, what are the chances of having the EXACT SAME # of particles AND Temperature?
Not so much
Let's look @ what's useful from our lab...
PV = k
if and only if (iff): n (# of particles) and T (temperature) are constant
From the transitive property:
if two things are equal to the same thing, then they are equal to each other.
So...
P V = K
1
1
P V = K
2
2
Then...
P V = P V
1
1
2
2
On your gas law summary chart...
Complete the section for Boyle's Law
This is what is commonly referred to as Boyle's Law
Quick check:
100 kPa x 25 mL = P x 50mL
2
if you double the volume, what is your new pressure?
Today in Lab:
There will be 3 different temperature baths
You will place the flask in the bath, let temp stabilize,
record temp and look at pressure
But first...
Let's look at temperature
But really first, in order to understand temperature, we need to understand kinetic molecular theory...
Kinetic Molecular Theory
I need volunteers...
You will are now members of the kinetic molecular theory demonstration team. You will be demonstrating upon command for, us the motions of paticles in the 3 states of matter we have looked at thus far.
1st: solid
2nd: heat up the temperature liquid
3rd heat up the temperature even more to the point where you become gas
the bonds between the particles are strongest
still motion as molecules vibrate in place
bonds present?
Yes but they easily break and re-form
most energy
kinetic means?
motion
molecular?
molecules
so it's literally the movement of molecules theory
no bonds
What are the particles doing with the sides of their container?
bump
So far, what variables' relationships have we analyzed in lab?
(what did we vary, what did we measure and what did we hold constant?)
In Thursday's lab:
varied volume
measured pressure
held temperature and n (# of particles) constant
In Monday's lab:
varied temperature
measured pressure
held volume and n (#of particles) constant
As volume increased, what happened to pressure?
pressure decreased
As temperature increased, what happens to pressure?
pressure increases
What is necessary to do to all other variables in order to analyze the relationship between two variables?
constant
From the lab last time...what kind of a relationship is there between pressure and temperature?
As temperature increases, pressure increases. As temperature decreases, pressure decreases.
Which type of a relationship is this...inverse or direct?
direct. As one increases, the other increases.
How?
proportionally!
How can you explain how this works in terms of molecular velocity and collisions of particles?
As temperature increases, kinetic energy increases and when energy increases, molecular velocity increases and # of collisions of particles increases. Remeber that gas pressure comes from the collisions of the particles with the walls of the container.
What was your equation using P, T, and k?

P = (T)(k)
where T is measured in Kelvins
If...
k = P
1
T
1
and
k =
P
2
T
2
What can you say about P T and P T ?
1
1
2
2
sticks.
sticks.
P
T
=
P
T
1
1
2
2
remember: if two things equal the same thing, then what can you say about their relationship to each other?
If 2 things equal the same thing, then those two things must also equal each other.
That's Gay-Lussac's Gaw Law.
Write this in the space provided on your gas law summary chart...
What variables did we analyze the relationship between?
temperature and Pressure
What variables did we hold constant (control)?
If we want to analyze the relationship between 2 variables, what must we do to all other variables?
keep all other variables constant
What do we call this in science? (remember from day 1 guided notes...)
control
n and V
What was a possible source of error in your lab method which would not allow for n to remain constant?
1. Get out outline
2. Get out lab notebook
3. Have a whiteboard and pen
4. Have out gas law summary chart
Feb 12
A high-pressure ridge sitting atop the Sochi area is to blame: the ridge is warming Sochi by decreasing cloudiness, keeping the skies clear and sunny.
Why is it so warm in Sochi?
The nearby mountains stay cooler, thanks to their elevation of more than 6,500 feet (2,000 meters) above sea level. But even the chilling effects of altitude aren't helping during this week's high temperatures, which have caused some puddles near the ski jumps.
While the winter warmth isn't unusual for Sochi, many former winter Olympic venues may not be cold enough to host the games by mid-century. The reason: global warming, a recent study found.
It's a beach town (right on black sea) but also...
write this in your lab notebook:
write this in your lab notebook
Why is it necessary in this lab to use absolute temperature?
You can't have negative temperature readings!
Let's try an example using Gay Lussac's Law
P
= 25 kPa
1
P
2
= 50 kPa
T
1
= -36 C
What is T
2
?
- 72 C
Does that make sense?
No
Why?
As temperature increases, pressure increases.
That is saying the opposite.
Remember...What is temperature a measure of?
average kinetic energy of molecules
As average kinetic energy of molecules increases, what happens to the # of collisions?
They increase.
As temperature increases, what happens to avearge kinetic energy of molecules?
increases energy as temperature increases
As collisions increases, what happens to the gas pressure?
gas pressure comes from the collisions of molecules with the sides of their container...
So...more collisions = ?
more collisions of molecules w/ sides of container = more gas pressure
temp
=
energy
=
collisions of molecules w/ sides of container
=
gas pressure
Okay, maybe you don't really care that much about the Olympics and the weather in Russia...
Let's talk about what's happening here in our neck of the woods...
Let's talk first about air pressure...
as air sinks...air pressure increases
as air rises...air pressure decreases
if air is rising, this allows for air to come in from the side (horizontally) from other places. What do we call that?
that'd be wind.
So...if the barometer drops, storm is coming.
If air is rising (we know that because the pressure is dropping (or has dropped)
That allows air from other places...
in the next couple of days, warm, tropical air coming in. not good snow.
But...this weekend, we're going to see colder air coming in so good snow Sat and Sun! :)
So, because the pressure is high...What is happening to air?
it's sinking...
So no air is coming in from other places. No storm. Sunny weather.
In the graphing of the lab data...
Which type of relationship is exhibited by temperature and pressure (direct or inverse)?
direct.
Now if we know they're directly proportional...is does the graph exhibit a directly proportional relationship?
No, it tells us that it's linear.
Why isn't it a directly proportional relationship?
The y-intercept is not zero (the line doesn't go through the origin)
So is degree celsius proportional?
it's all relative!
Celsius not proportional
So far we've analyzed the relationship between pressure and temperature
and
volume and pressure
Let's take a look @ volume and temperature
I have here two balloons. Their size is as close to each other as I can...
I'm going to place them in water baths of different temperatures...
First, what am I keeping constant (controlling)?
n (# of particles)
and?
pressure. the pressure in this room is going to stay the same
What normally happens to volume when it's in the cold?
lesser
Okay, let's try it.
Now, I've put both balloon in water baths...
What happens when I switch them (take the hot one and put it in the cold one and the cold one and put it in the hot one)?
The one placed in the cold water shrinks and the one in the hot water expands.
Using the term volume?
As temperature increases, volume increases, as temperature decreases, volume decreases
What kind of relationship is this (as temperature increases, volume increases and as temperature decreases, volume decreases)?
direct
How?
proportionally!
brought it back again!
Now you...suggest -on ur whiteboard- an equation for this new law (whose law is it?)
Charles' Law
V
1
T
1
=
V
2
T
2
If they're direct, which side of the equation will we expect V and T?
opposite side!
Ok, now you complete this on your summary sheet...
Now...using the relationships we've determined...write an equation - on your pressure inquiries page combing all 3 gas laws...
P
1
V
1
T
1
=
P
T
V
2
2
2
This is referred to as the combined gas law
Go ahead and write this on your gas law summary sheet.
What must we keep constant here?
n
What does our temperature always have to be in?
kelvins (K)
A closed container at constant temperature is compressed to two-thirds its original volume. What happened to the pressure inside the container?

relationship between pressure and volume?
inverse
So if volume is decreased by 2/3 then pressure must be increased by the reciprocal...3/2
The plunger of a syringe is pulled out and the volume changes from 20 mL to 25 mL. What is the pressure inside the syringe if the original pressure was 100 kPa?

Relationship between volume and pressure?
inverse. as volume decreases, pressure increases
So if volume increases, pressure must decrease. Right now you know that if you had any pressure greater than 100 kPa...that's not right.
Let's talk about the work you use to solve these.
(examples from audience)
How to show your work****
****ON THE TEST, NOT SHOWING WORK WILL BE DISCOURAGED THROUGH THE USE OF WITHHOLDING POINTS FOR WORK NOT SHOWN
Step 2. Write the relationship
Step 3. Solve for the unknown
3. Now you do the math
Now, the thinking:
our example:
pressure and volume inversely related
P
V
1
1
=
P
V
2
2
P
2
= ?
P
2
=
V
1
V
2
P
1
A container with a movable piston has a volume of 1.5L at 1 atm. What happens to the volume if the pressure is decreased to 0.60 atm at a constant temperature?

Quiz 9.4
Now that you know what is expected of you in terms of showing work...
A flask is sealed at STP. What happens to the pressure inside the flask if the temperature is increased to 50.°C?

1.
2.
3.
A 0.0500 L sample of gas has a pressure of 0.96 atm at 26.4°C. The temperature is changed until the final pressure and volume of the gas are 1.06 atm and 0.0624L, respectively. What is the final temp?

6 points
6 points
7 points
What's happening?
3rd period - exit ticket check-in...How'd you do?
Did you show the work required?
4th period exit ticket check-in...What work is required to be shown?
Notes on your exit ticket...
Quiz 9.3 - Some Gas Law work/practice
Ideal Gas Law...
Avogadro's Law
2/18/2014
Tues
Rally!
get out outline. I'll be checking during quiz.
The Ideal Gas Law
With the combined gas law, what must we hold constant?
think. partners. sticks.
n = number of moles
Please grab a whiteboard on your way in.
What are the four variables we're analyzing for gases?
think. partners. sticks.
pressure
temperature
volume
# of particles (moles!)
Enter the ideal gas law...
Write the combined gas law.
V P
T
1
1
1
=
V
2
T
P
2
2
Hint: What can you say about the proportionality between the number of moles and the number of particles?
directly proportional
Which have we not yet analyzed?
n
First, we need to look at the relationship between n and volume.
We know the volume of 1 mole of gas = ?
1 mole of gas = 22.4 L
at STP of course!
Here I have a balloon...What happens to the volume if I put more particles in it?
volume increases as particles increase
What if I decrease the number of particles by 1/2?
volume decreases by 1/2
11.2 L = 0.5 moles
What is the relationship between n and V?
if n increases, V increaes
How?
proportionally!
directly proportional
Avogadro's Hypothesis
Look in your notes...when did we talk about Avogadro's Hypothesis?
equal volumes of gases at the same temperature and pressure contain equal numbers of particles
What happens to the volume of an expandable container if the temperature increases from -15°C to 20.°C at constant pressure? The volume of the container was initially 2.0 x 10 L

We learned that a mole of gas @ STP = 22.4 L
STP =?
1 atm
273 K
whiteboards
at same temp and pressure...
think. sticks.
One mole of any gas at STP is 22.4 L
organization mini-test for candy.
1st person to find and hold it up to show me gets candy!
Hint: mole island/dimensional analysis intro unit stuff
Balloon drawing time
1. Draw this unblown-up balloon.
2. After I blow up the balloon, what happens?
At the particle level, why does the balloon get bigger?
Do the size of the arrows change?
Why?
Why are there the same # of arrows pushing on the outside of the balloon in both drawings?
When you increased the number or particles, it increased pressure greater than outside so to equalize with outside pressure, the volume of the balloon had to increase.
What do we have to control in this law?
n
n
1
2
Don't use this...
PV = nRT
Use this:
Now, you figure out R
R = PV / nT
use kPa = 101.35
What do we know?
volume of 1 mole of gas @ STP
What's happening?
1. 4th period - turn in quiz 9.4

2.Quiz 9.5

2. Balloon Drawings - What's going on there?

3. Avogadro's Hypothesis

4. Ideal Gas Law

5. What happens when real life happens? (why gases aren't just ideal...)
6. Under pressure...Dalton's Law of Partial Pressures
Feb 20
What is it?
What is STP?
0 degrees C
101.35 kPa
but wait, if we're looking at proportions, can we use a non-proportional temperature scale.
no way, gotta use Kelvins so it's proportional
solve for R
What did you get?
Solving PV = nRT for R...
R = PV
nT
P = 101.35 kPa
V = 22.4 L
remember, that's the molar volume of 1 mole of gas @ STP
n = 1
T = 273.15 K
R =
(101.35 kPa)
(22.4 L)
(1 mol)
(273.15 K)
=
8.31130771
kPa L
mol
K
Analyzing the inverse and direct relationships...
PV = nRT
Pressure and volume?
inverse
Pressure and temperature?
direct
Pressure and # of moles?
direct
Volume and Temperature?
direct
Volume and # moles?
direct
temperature =?
average kinetic energy
as temperature increases, so does energy and as energy increases, so do # of collisions, remember gas pressure ?
come from # of collisions of gas particles with walls of containers
so more collisions = more pressure
What about R?
That's your constant
of what?
Proportionality!
The atmosphere of Earth is a mixture of 78.084% N , 20.946% O , 0.934% Ar, and 0.033% CO by volume when the water vapor has been removed.
What image does this description evoke in your mind?
Do you think this is a homogenous or heterogeneous mixture of gases?
2
2
2
it's a homogenous mixture of course
ie: it doesn't look like this!
Gases expand to fill their containers...
When we describe the atmosphere as 20.946% Oxygen by volume, we mean that the volume of the atmosphere would shrink by 20.946% if the Oxygen is removed.
What about the pressure of the different gases in your room? Is the pressure of the Oxygen in the atmosphere the same as the pressure of the Nitrogen?
think. partners. whiteboards.
According to the ideal gas equation, the pressure of a gas is proportional to the number of moles of gas, iff the temperature and volume are held constant. Because the temperature and volume of the O and N in the atmosphere are the same, the pressure of each gas must be proportional to the number of the moles of the gas. Because there is more N in the atmosphere than O , the contribution to the total pressure of the atmosphere from N is larger than the contribution from O .
2
2
2
2
2
2
PV = nRT
The name's Dalton...John Dalton
Chemist John Dalton was born September 6, 1766, in Eaglesfield, England. During his early career, he identified the hereditary nature of red-green color blindness. In 1803 he revealed the concept of Dalton’s Law of Partial Pressures. Also in the 1800s, he was the first scientist to explain the behavior of atoms in terms of the measurement of weight. Dalton died July 26, 1844 in Manchester, England.
No, no, not Timothy Dalton who played James Bond...
John Dalton!

John Dalton was the first to recognize that the total pressure of a mixture of gases is the sum of the contributions of the individual components of the mixture.
By convention, the part of the total pressure of a mixture that results from one component is called the partial pressure of that component.
Dalton's law of partial pressures states that the total pressure of a mixture of gases is the sum of the partial pressures of the various components.
Dalton's Law in Real Life...
Dalton made an assumption when developing his law; that gas molecules act independently of one another.
This assumption is true:

when there is a lot of space between gas molecules

when the temperature is not too low

This is the same assumption that was made for the Ideal Gas Law.

Let’s take a look at a real world application of Dalton’s Law of Partial Pressures; the gas that a diver breathes has to have a Partial Pressure of 0.21 atm of Oxygen.
If the Oxygen level is higher, poisoning could occur and if the level is lower, the diver could die from suffocation. The valve on the diver’s tank is designed to maintain the Oxygen level by adding Helium when there is too much Oxygen.
When a scuba diver dives, the increased pressure causes N (g) to dissolve in the blood.
If a diver rises too fast, the dissolved N will form bubbles in the blood, a dangerous and painful condition called "the bends".
Helium, which does not dissolve in the blood, is mixed with O to prepare breathing mixtures for deep descents.

A scuba tank contains O2 with a pressure of 0.450 atm and He at 855 mm Hg. What is the total pressure in mm Hg in the tank?


1. convert atm to mmHg
2. Calculate the sum of the pressures.
For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mm Hg, what is the partial pressure of the helium?

1 atm = 760 mmHg
no.
2
2
2
Nitrox = mixture of oxygen and nitrogen gases
Let's talk about being real...
The main flaw in the ideal gas model is the assumption that gas molecules do not attract or repel each other. Attractions and repulsions are negligible when the distance between molecules is large, but they do become larger as the molecules become closer together. If you can contrive conditions that force the molecules into close contact, so that attractions and repulsions can't be neglected, you will likely see deviations from ideal behavior.
Since molar volume V/n = RT/P, decreasing the pressure and/or increasing the temperature will cause the molecules to move farther apart on average. That should cause the gas to behave more ideally.
Real gases that is!
Now, time to work on gas laws worksheet #1
#2 is your homework. Due next class.
Also, finish your outline
Steven Chu

Born 28 Feb 1948.

American physicist who (with Claude Cohen-Tannoudji and William D. Phillips) was awarded the 1997 Nobel Prize for Physics for their independent, pioneering research in cooling and trapping atoms using laser light. In their normal state the constant random thermal motion of atoms limits precise measurements of atomic states. Thus, physicists sought to cool and slow atoms down as much as possible. Chu used six laser beams and worked with a hot gas of sodium atoms. He managed to cool and trap atoms in what he called “optical molasses.” By 1985, he had cooled sodium atoms to a temperature of about 240 millionth of a degree above absolute zero. The atoms could be trapped in the laser beams for a period of about half a second. He was chosen by President Obama to become the 12th U.S. Secretary of Energy (2009-2013).
by Daniel C. Tsui
http://todayinsci.com/2/2_28.htm#ReaumurRene
read more here!
(What relationship do we have?)
____________
linear
Besides that, it's?
_________________
Give an equation to represent this sitaution:
step 1: Determine variables

w =

h =
wage
hours worked
Step 2: Prior Knowledge
How do we write the equation of a line in math?
y = mx + b
Our Equation:
Instead of x and y, what variables are we using?
w and h
Which is the x?
Which is the y?
hours worked
wage
How is this equation different from our model equation (the equation from math that you wrote for the equation of a line)
w = 8.5h
Our equation doesn't have a b. What is b?
y-intercept
(where the line crosses the y-axis)
Now what is the 8.50 in our equation called?
slope
I
n general, in science , we call this the ________ (constant of ______________).
constant
proportionality
So we can say k =
y
x
or in our case
w
h
What is K = the formula of?
slope!
Another way to say this is that it is a direct __________.
proportion
This is a _____ relationship.
direct
Summary - Direct Relationship (proportion)
y = kx
k = y
w = kh
k = w
x
h
in terms of x and y?
in terms of x and y?
set amount you make in 1 year
I make $48,000 per year
How much do I make per hour?
Discuss with your partner.
Step 1: How many days am I working?
Step 2: How many hours per day do I work?
Step 3: How much do I make in 1 day?
193 days = 1 year
7 hours = 1 day
$48,000
x
1 year
193 days
1 year
x
7 hours
1 day
=
$
hour
35.5
On average, I work 10 hours per day.
How much do I make per hour?
At that rate, I make $24.87 dollars
1 hour
Please calculate the amount made per hour for if the teacher worked different hours in a day from 1-12 hours.
Please plot the amount made per hour for hours worked in 1 day from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
For a salary job, what happens to the amount I make per hour as I work more hours in a day?
the amount made per hour decreases
Write an equation for what you've shown on your graph.
w = 249
Graph the amount made per hour compared to the number of hours worked in 1 day on the graph provided.
(sticks for whose goes on the doc camera)
3
direct relationships?
inverse relationships?
c =
d=
m =
cats
days
mice
If we keep 5 cats, only give them 1 day, how many mice should they catch?
5 cats can catch 5 mice in 5 days.
h
cats
days
mice
5
5
5
1
What are we keeping the same?
number of cats
How much less time do we have?
1/5
How much less mice can they catch?
1
What did we keep constant?
cats
What is the relationship between days and mice?
As days increase, number of mice caught increases.
What do we call this?
direct
1/5
1
5
5
1
c
d
m
5 5 5
5 1 1
1
How long does it
take 1 cat to catch
1 mouse?
What is constant?
mouse
1
What is the relationship between cats and days?
less cats, takes more days to catch same amount of mice
What type is that?
inverse
1
5
5
x
x
5
c d m
5 5 5
5 1 1
1 5 1
3
3
How many days does it take
3 cats to catch 3 mice?
What is the relationship
between cats and days?
inverse
increasing number of cats decreases the days they need to catch mice.
3 times the amount of cats will catch 3x the amount of mice in the same time.
5
Gas and Pressure Reference Sheet
Pressure is:
P = F
A
The force exerted by the substance per unit area on another substance.
What causes gas pressure?
collisions of gas particles with
walls of the container
How is gas
pressure
increased?
decrease the area
hint: think of the pressure equation you just wrote
less space for particles = more pressure
Why?
What causes gas pressure?
collisions of gas particles with walls of container
if you make the container smaller (decrease the area) you will have more collisions of particles with the walls of their container.
What happens as you decrease area?
What happens to pressure as you increase area?
(make the container smaller)
What happens to pressure when...
(make the container bigger)
decreases
increases
From our class about cats eating mice, please complete the following questions:
In order to sudy the relationship between 2 variables, the 3rd variable must be held ___________.
What is a basic rule you can state for equations involving only multiplication (not division). This rule can easily tell you by looking at an equation with only multiplication whether 2 variables are directly or inversely proportional.
constant
same side = inversely proportional
opposite sides = directly proportional
y = kx
xy = k
What is K?
constant
Drawing at the Particle level:
More pressure outside "pushes" the index card up onto the cup.
Pressure Conversions:
Standard atmospheric pressure = 1atm
1 atm = 101.35 kPa
760 mmHg = 1 atm
Boyle's Law
Variables:
Pressure and Volume
Constant:
Temperature
Pressure
Volume
increases
decreases
decreases
increases
What type of relationship is this?
inverse
When writing an equation, which side of the equal sign should the V and P be on?
same side
K = VP
specific equation
general eqn
P V = P V
1
1
2
2
Charles' Law
variables:
Volume and Temperature
Constant:
pressure
Volume
Temperature
increases
increases
decreases
decreases
What type of relationship is this?
direct
Which side of the equal sign should the V and T be on?
opposite sides
How did we show that for the direct relationship (hourly pay)?
division
K =
V
T
V
T
V
=
T
1
2
1
2
Gay-Lussac's Law
Variables:
Temperature and Pressure
Control:
Volume
Temperature
Pressure
increases
increases
decreases
decreases
What kind of relationship is this?
direct
When we write an eqution for the relationship between temperature and pressure, which sides should the T and P be on?
opposite
How can we show this relationship so that they are on the same side and k is on the other side of the =?
K
=
P
T
Can you write an equation to show a comparison of P and T for two different situations (use 1 for initial and 2 for second)
Kinetic Molecular Theory
The gas laws developed by Boyle, Charles, and Gay-Lussac are based upon empirical observations and describe the behavior of a gas in macroscopic terms, that is, in terms of properties that a person can directly observe and experience.
OLD
STUFF

Not for spring 2015
Re-cap: Sticky Balloon
Why did the flexible cup stick to the balloon when you squeezed the sides?
What happens to the volume when you squeeze the cup?
decreased
Why does the cup stick to the balloon?
Hint: pressure
HintHint: What can you say about the volume when you let go of the cup?
increases
pressure inside cup is
less than outside pressure. Outside pressure is pushing balloon up onto cup.
Boiling Balloons:
What happens when the liquid boils?
some of the liquid changes state to gas
What was initially in the flask?
regular air (gas)
The water vapor replaces the air that was originally in flask.
What happens when you put the balloon over the flask?
the water vapor is trapped ( n = number of moles of gas)
Draw 4 pictures.
Before the balloon is put over flask.
After the balloon is put over the flask.
3 minutes after flask is off heat.
Flask after it cools to room temperature.
Draw @ the particle level!
warm-up 6.4
"The air we breathe"
What is the relationship between n (number of moles) and volume?
direct
What is our equation for this law, then?
When ammonium chloride is heated, it decomposes into ammonia and hydrogen chloride gas.
calculate the moles of ammonia and moles of HCl produced when 30 g of ammonium choloride decomposes completely.
What is the total volume of these two gases at 25 degrees Celsius and 1 atm of pressure?
NH Cl
4
(s)
NH
3
+
HCl
(g)
(g)
Step 1: write the equation
Step 2: Convert grams to moles
30 g
NH Cl
4
x
1 mol NH Cl
4
53.5 g NH Cl
4
=
0.56 mol NH Cl
4
Step 3: Convert moles of reactant to moles of product
0.56 mol NH Cl
4
How?
(mole ratio!)
x
1 mol NH
3
1 mol NH Cl
4
=
0.56 mol NH
3
0.56 mol NH Cl
4
x
1 mol HCl
1 mol NH Cl
4
=
0.56 mol HCl
Use the idea gas law to determine the volume of each.
PV = nRT
Solve for V
V = nRT
P
(.56 mol)
n = .56 mol
R = 8.31 L atm
K mol
.
.
T = 25 + 273 = 298 K
P =
1 atm
101.3 kPa
x
1 atm
= 152 kPa
(8.31 L atm)
K mol
.
.
152 kPa
)
(
(298 K)
=
9.12 L
The moles produced are the same because the mole ratios were the same so both gases have a volume of 9.12 L. Add them together for the total volume.
Total volume of both = 18.24 L
Number of particles (n)
Number of particles (n)
V T = V T
1
1
2
2
P T = P T
1
1
2
2
specific equation
general equation
V = K T
number of particles
specific equation
general equation
P = K T
Avogadro's Law:
- blowing up a balloon
variables: volume and number of particles (n)
constant: Temperature and Pressure
V
n
What type of relationship is this?
direct
general equation:
V = K n
specific equation:
V n = V n
1
1
2
2
P V T = P V T
1
1
2
2
2
1
All you need to know for the test:
All the gas laws are examples of ____________ relationships.
proportional
This means we need a proportional temperature scale.
___________ is a proportional temperature scale where temperature is directly proportional to _________ energy.
Kelvin
kinetic
Which side of the equals sign?
Proportional Relationship
inverse
direct
same
opposite
When one goes , the other goes?
On the test, you will be given the Ideal Gas Law:
It works @ STP
PV = nRT
direct (opposite sides)
direct (opposite sides)
direct (opposite sides)
invese
(same
side)
From the ideal gas law, you can use the direct and inverse relationships to create each individual gas law.
P and V
P and T
V and T
V and n
direct
direct
direct
inverse
same side
opposite side
opposite side
opposite side
P V = P V
1
1
2
2
P T = P T
1
1
2
2
V T = V T
1
1
2
2
V n = V n
1
2
1
2
Step 1: Determine which variables are changing (which law to use) and identify the variables.
If a gas at 25.0 degrees celsius occupies 3.60 L at a pressure of 1.00 atm, what will be its pressure at a volume of 1.44 L?
P and V
Plug in the value for each variable with units and solve!
Write the answer from your calculator and then determine the num of sig figs you get to report, then write your rounded answer with correct sig figs
P = 1.00 atm
P = ?
1
V = 3.60 L
1
V = 1.44 L
2
2
Full transcript