2014-2015 . Four Variables: Amount of gas Volume Temperature Pressure.

GAS LAWS2014-2015

http://www.nclark.net/GasLaws

MEASURING GASES Four Variables:

Amount of gas Volume Temperature Pressure

AMOUNT OF GAS (N) Quantity of gas in a given sample is

expressed in terms of moles of gas

n =mass = m (g)____ molar mass M (g/mol)

One mole of NaCl, = mass of 58.45 g. One mole of the liquid, = mass of 18.0 g and occupies a volume of 18.0 mL. One mole of the gas, = mass of 32.0 g and occupies a balloon whose diameter is 35 cm

VOLUME (V)

Gas uniformly fills any container in which it is placed

Volume of gas = volume of its container

Metric unit = L 1 L = 1000 cm3

TEMPERATURE (T)

Measured with thermometer in degree Celsius (˚C)

Must be converted to Kelvin temp scale No negative temps T (K) = T (˚C) + 273

PRESSURE (P)

Outward force of gas spread over the area of the container is called pressure

P = Force Area

Pressure = Pascal (Pa)

ATMOSPHERIC PRESSURE

Gases of atmosphere also exert pressure on everything come into contact with

(gas) density = Mass (of gas)

Volume

P = m V

Atmospheric Pressure decreases with height

PRESSURE CONVERSIONS

STP means standard temperature and pressure

1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr =101,325 Pa = 14.69 psi

***all of these equal each other!***

Temperature: 0 ˚C or 273 K

GAS LAWS Charles’ Law (slide 4)

Boyle’s Law (slide 31)

Guy Lusaac’s Law (slide 77)

LeChatelier’s Principle (slide 105)

Ideal Gas Law (slide )

CHARLES LAW

CHARLES’S LAW

Volume of a gas increases with temperature. (Gases expand with heat).↑ T = ↑ V ↓ T = ↓ V

*Constant amount of gas at a constant pressure

Jacques Charles proposes Charles's Law. 1787

The formula for the law is:

V1/T1 = V2/T2

Where: V1 is the initial volume T1 is the initial temperature

V2 is the final volume T2 is the final temperature

***temperature MUST be in Kelvin (absolute zero) NOT oC or oF!***

DEMONSTRATION

- Balloon in hot and coldwater

--What happens??

- Glass bottle with balloon in hot water

Demonstration: Fit a balloon to the top of a glass bottle and place in pan with water. Place on top of heat source and observe.

This law means that when the temperature goes up, the volume of the gas goes up.

This law means that when the temperature goes up, the volume of the gas goes up.

When the temperature goes

down, the volume of the gas decreases.

http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/gaslaw/charles_law.html

Key Concept ~ When the temperature of a gas is increased, its volume will increase. Students will be micro waving small amounts of

popcorn in a clear bowl. Popcorn pops when the moisture inside boils and

expands, bursting the kernel open. Instructions: Place about two tablespoons of popcorn

in the clear plastic bowl. Put the top on the bowl and place in the microwave.

microwave on high and observe Questions: Describe what you see (yeah, I know, but

try). What do you think makes the popcorn pop? Put your popcorn in a paper bag and then squirt in some butter if you wish.

Station 2 Microwave Popcorn

Station 9 Super Duster & Office Buster Key Concept ~ When the volume of a gas increases, its

temperature will decrease.

Obtain a can of compressed "air," such as those used to clean electronic equipment. As you depress the nozzle, the gas inside (typically an HFC) responds to the reduced pressure by "boiling" or rapidly turning into a gas. This is an endothermic process so the can gets extremely cold (can even cause frost-bite if you hold it too long.) I like the students to relate this to the phenomenon of water boiling at lower temperatures at high altitudes due to the lower pressure. (Lots of campers know this very well.)

The classic Drinking Bird uses a similar concept and makes a good companion to this station.

See more at: http://www.arborsci.com/cool/chemistry-gas-laws-smorgasborg#sthash.Qy9PndDT.dpuf

http://www.arborsci.com/cool/chemistry-gas-laws-smorgasborg#sthash.Qy9PndDT.dpuf




When temperatures get colder, you may need to add some more molecules to get the safe PSI for your vehicle.

Copyright © 2010 Ryan P. Murphy

Other Examples Of Charles’ Law

You may notice that your sports equipment doesn’t work well when you go out into your garage in the winter. The air molecules are moving very

slowly so the ball is flat.


A 2.0L sample of air is collected at 298 K and then cooled to 278 K. The pressure is held constant at 1.0 atm.

a. Does the volume increase or decrease?b. Calculate the volume of air at 278 K.

Step One: Write down the information given and check units.

Step Two: Write down the correct formula.

Step Three: Plug the given information into the formula and solve for the unknown variable.

Step Four: Record the two answers.

V1 = 2.0L V2= ?T1 = 298 K T2 = 278 KP1 = 1.0 atm P2 = 1.0 atm

change

same

V1/T1 = V2/T2

V1/T1 = V2/T2

2.0 =

V2

298 278(2.0)(278) = V2 (298)

298 298

a. The volume will decreaseb. V2 = 1.9L

BOYLE’S LAW

BOYLE’S LAW: Pressure and Volume are inversely proportional.

↓ volume = ↑ pressure↑ volume = ↓ pressure

1662, Robert Boyle

BOYLE’S LAW

Inverse ↑ P : ↓ V

Formula: P1V1 = P2V2

* a constant amount of gas

* constant temperature

This works because, if the volume of a container is increased, there is a greater area in which the particles of gas inside the container can move. Since the particles have more space, there is less force exerted on the walls of the container by the particles and therefore, less pressure.

Very Important! Record in Journal.

Activity! Syringes

Activity! Syringes

Depress plunger on the syringe.

Activity! Syringes Depress plunger on the syringe. Cover hole with finger.

Activity! Syringes Depress plunger on the syringe. Cover hole with finger. Try and pull handle (gently please).

Why is it difficult?Keep thumb on opening.

Activity! Syringes Answer: It was difficult because your

finger created a sealed vacuum and prevented air from entering the chamber.

Keep thumb on opening.

Activity! Syringes Answer: It was difficult because your

finger created a sealed vacuum and prevented air from entering the chamber. Atmospheric pressure is 1 kilogram per square centimeter at sea level. Keep thumb on

opening.

Activity! Syringes (Opposite)

Activity! Syringes (Opposite) Fill syringe.

Activity! Syringes (Opposite) Fill syringe. Cover hole with finger.

Activity! Syringes (Opposite) Fill syringe. Cover hole with finger. Try and push handle (gently please).

Activity! Syringes (Opposite) Fill syringe. Cover hole with finger. Try and push handle (gently please).

How does this represent Boyles Law?

Activity! Syringes (Opposite) How does this represent Boyles Law?

Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger,

you increase pressure and the volume of the gas is decreased.

Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger,

you increase pressure and the volume of the gas is decreased.

Please determine how many milliliters you were able to compress the gas inside using the numbers on the syringe.

Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger, you

increase pressure and the volume of the gas is decreased.

Please determine how many milliliters you were able to compress the gas inside using the numbers on the syringe.

Answer: You should be able to compress the gas to about 50% of it’s starting volume by hand and then it gets difficult.

“Can’t wait to eat my yogurt.”

As you inhale, your diaphragm flattens out allowing your chest to expand and allows more air to flow into your lungs.

As you inhale, your diaphragm flattens out allowing your chest to expand and allows more air to flow into your lungs. Air pressure decrease, air then rushes

into your lungs.

As you exhale, your diaphragm relaxes to a normal state. Space in chest decreases.

As you exhale, your diaphragm relaxes to a normal state. Space in chest decreases. Air pressure increases, air then rushes

out of your lungs.

Which is a inhale, and which is a exhale?

A B


InhaleA B


Inhale ExhaleA B


A BA B


InhaleA BA B


Inhale ExhaleA BA B

The Bends (Decompression Sickness) – Bubbles form in blood if you rise to quickly because of the rapid decrease in pressure.


The Bends (Decompression Sickness) – Bubbles form in blood if you rise to quickly because of the rapid decrease in pressure. A diver must save time to travel to

surface slowly so body can adjust.


What pressure is required to compress 196.0 liters of air at 1.00 atmosphere into a cylinder whose volume is 26.0 liters?


P1 = 1 atm V1 = 196 L, P2 = ? V2 = 26 L


P1V1 = P2V2Step Three: Plug the given information into the formula and solve for the unknown variable.

(1 atm) (196 L) = (P2) (26 L)P2 = 7.5 atm

Freon-12 was a widely used refrigerant but has been replaced by other refrigerants that do not lead to the breakdown of the ozone layer. Consider a 1.5 L sample of Freon-12 gas at a pressure of 56 torr. If the pressure is changed to 150 torr at a constant temperature….

a. Will the volume of gas increase or decrease?b. What will be the new volume of the gas?



Step Three: Plug the given information into the formula and solve for the unknown variable.

Step Four: Record the two answers.

V1 = 1.5 L V2= ?P1 = 56 torr P2 = 150 torr

P1V1 = P2V2

P1V1 = P2V2

(56)(1.5) = (150)(V2)150 150 a. The volume of gas will

decreaseb. V2 = 0.56 L

GUY- LUSAAC’S

LAW

GUY LUSAAC’S LAW

French chemist Joseph Louis Guy-Lussac in 1802

= the pressure of a fixed mass and fixed volume of a gas is directly proportional to the gas's temperature

↑ temperature = ↑ pressure↓ temperature = ↓ pressure

P/T=kWhere: P is the pressure of the gasT is the temperature of the gas (in kelvins)k is a constant

When comparing two substances:

P1/T1=P2/T2

As pressure increases, temperature increases.


As pressure increases, temperature increases.

As pressure decreases, temperature decreases.


This photoshop job might look “Funny”.

Caution! Graphic Images of burns / the dangers of pressure and temperature.

The consequences of severe burns and explosions are not “funny”.


BOILING WATER AT ROOM TEMPERATURE

↑ pressure =↑

temperature

Describe what should happen?

What does happen?

EXAMPLE:Five grams of octane (C8H18) and enough oxygen to burn it are in an automobile cylinder compressed to 20 atm at 28°C. The mixture explodes and heats the cylinder to 150°C. What is the pressure in the (same sized) cylinder after the explosion?P1 = 20 atm T1 = 301K,P2 = ?T2 = 423 K

P1 / T1 = P2 / T2

(20)/(301) = (P2)/(423)

P2 = 28.4 atm

EXAMPLE 2A 20 L cylinder containing 6 atm of gas at 27 °C. What would the pressure of the gas be if the gas was heated to 77 °C?

P1 = T1 = P2 = T2 =

P1 / T1 = P2 / T2


P1 = 6 atm T1 = 27 +273 = 300KP2 = ??T2 = 77+273 = 350K

P1 / T1 = P2 / T2


P1 = 6 atm T1 = 27 +273 = 300KP2 = ??T2 = 77+273 = 350K

P1 / T1 = P2 / T2

(6 atm) x (350K) = (P2)(300K)

P2 = 7atm

PRESSURE CONVERSIONS

STP means standard temperature and pressure

1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr =101,325 Pa = 14.69 psi

***all of these equal each other!***

Temperature: 0 ˚C or 273 K

2014-2015 . Four Variables: Amount of gas Volume Temperature Pressure.

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