The GAS LAWS The GAS LAWS

Gases have mass Gases diffuse Gases expand to fill

containers Gases exert pressure Gases are compressible Pressure & temperature are

dependent

Gases have mass Gases diffuse Gases expand to fill

containers Gases exert pressure Gases are compressible Pressure & temperature are

dependent

Gas PropertiesGas Properties

Volume (V)• Units of volume (L)

Amount (n)• Units of amount (# of molecules)

Temperature (T)• Units of temperature (K)

Pressure (P)•Units of pressure (mmHg)•Units of pressure (KPa)•Units of pressure (atm)

Volume (V)• Units of volume (L)

Amount (n)• Units of amount (# of molecules)

Temperature (T)• Units of temperature (K)

Pressure (P)•Units of pressure (mmHg)•Units of pressure (KPa)•Units of pressure (atm)

Gas VariablesGas Variables

What is Pressure?

Pressure is the amount of force per unit area.

The Units of Pressure are N/m2 or Pascals (Pa)

Pressure is the amount of force per unit area.

The Units of Pressure are N/m2 or Pascals (Pa)

area

forcepressure

How is pressure created by gas molecules?

A gas is made up of various molecules. These molecules move around and collide with each other and the walls of their container. Gas molecules exert pressure on any surface with which they collide.

A gas is made up of various molecules. These molecules move around and collide with each other and the walls of their container. Gas molecules exert pressure on any surface with which they collide.

What is atmospheric Pressure?

Atmospheric pressure Atmospheric pressure is the pressure created is the pressure created by the mass of the gas by the mass of the gas molecules in the air molecules in the air being pulled to the being pulled to the surface of the Earth.surface of the Earth.

Atmospheric pressure Atmospheric pressure is caused by the mass is caused by the mass of air that is pulled of air that is pulled down by gravity. The down by gravity. The weight of air creates a weight of air creates a force.force.

Air pressure can varyAir pressure can vary

Atmospheric pressure Atmospheric pressure is the pressure created is the pressure created by the mass of the gas by the mass of the gas molecules in the air molecules in the air being pulled to the being pulled to the surface of the Earth.surface of the Earth.

Atmospheric pressure Atmospheric pressure is caused by the mass is caused by the mass of air that is pulled of air that is pulled down by gravity. The down by gravity. The weight of air creates a weight of air creates a force.force.

Air pressure can varyAir pressure can vary

One Square inch of

atmosphere weighs

14.7lbs.14.7lbs.

How does that pressure feel?

The behavior of a gas depends very strongly on the temperature and the pressure of the gas.

To make it easier to discuss the behavior of a gas, it is convenient to designate a set of standard

conditions, called STP.STP.

Standard Temp and Standard Standard Temp and Standard PressurePressure

Standard Temperature = 0°C or 273KStandard Temperature = 0°C or 273K

Standard Pressure =1.00 atm or 760 mmHg or Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa 101.3kPa

The behavior of a gas depends very strongly on the temperature and the pressure of the gas.

To make it easier to discuss the behavior of a gas, it is convenient to designate a set of standard

conditions, called STP.STP.

Standard Temp and Standard Standard Temp and Standard PressurePressure

Standard Temperature = 0°C or 273KStandard Temperature = 0°C or 273K

Standard Pressure =1.00 atm or 760 mmHg or Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa 101.3kPa

Why is a mmHg called a Why is a mmHg called a TorrTorr??

Evangelista Torricelli was born in Italy in 1608. He investigated the phenomenon of the inabilityinability of water pumps to raise water more than 33 feet.

The theory was that nature “abhorred a vacuum” and when a pump created a vacuum above a water surface the water rushed in to relieve the empty space.

Torricelli inverted a 4-foot tube

filled with mercury in a bowl of mercury and found that the level only dropped to about 30 inches above the bowl.

This left a unfilled vacuum above the liquid.

Evangelista Torricelli was born in Italy in 1608. He investigated the phenomenon of the inabilityinability of water pumps to raise water more than 33 feet.

The theory was that nature “abhorred a vacuum” and when a pump created a vacuum above a water surface the water rushed in to relieve the empty space.

Torricelli inverted a 4-foot tube

filled with mercury in a bowl of mercury and found that the level only dropped to about 30 inches above the bowl.

This left a unfilled vacuum above the liquid.

Torricelli invented the barometer

Torricelli had demonstrated that air had weight and exerted pressure.

He also noted that the level of mercury in the tube changed from day to day!

The 1st weather man…

Torricelli had demonstrated that air had weight and exerted pressure.

He also noted that the level of mercury in the tube changed from day to day!

The 1st weather man…

What does the invention of the Barometer mean?

That ….

NOTHING SUCKS!That ….

NOTHING SUCKS!

The Vacuum Sweeper your mother keeps

telling you to use doesn’t SUCK!

YOU don’t even SUCK face when

you Kiss!

So if nothing Sucks(Pulls) what happens?

Everything …..

PUSHES!!

Everything …..

PUSHES!!

Let’s look at how a straw works.

Gas molecules always move from high to low areas of pressure.

As you “Suck” on the straw you create a low pressure in your mouth. The High atmospheric pressure then PUSHES the fluid up the straw into the mouth.

Gas molecules always move from high to low areas of pressure.

As you “Suck” on the straw you create a low pressure in your mouth. The High atmospheric pressure then PUSHES the fluid up the straw into the mouth.

Low

Pres

sure

High atmospheric Pressure

Mouth

must

mak

e a

seal

Pressure

Pressure always pushes pushes from high pressure to low

pressure.

We measure the amount of push using a closed manometer

A closed manometer is the same as Torricelli’s barometer.

Pressure always pushes pushes from high pressure to low

pressure.

We measure the amount of push using a closed manometer

A closed manometer is the same as Torricelli’s barometer.

P1V1 = P2V2P1V1 = P2V2

Boyle’s law•In a fixed amount of gas the Pressure of the gas is inversely proportional to its volume when the temperature remains the same.

•as P then V•at constant T, n

Boyle’s law•In a fixed amount of gas the Pressure of the gas is inversely proportional to its volume when the temperature remains the same.

•as P then V•at constant T, n

The LAWSThe LAWS

Boyle’s Law

Boyles law in action!

Try the Demo and record three values for P and V

How about a submarine??Navy site try it!

Boyles law in action!

Try the Demo and record three values for P and V

How about a submarine??Navy site try it!

A Boyle’s Law Problem

Freon-12, (CCl2F2), is used in refrigeration systems. What is the new volume (L) of a

1.6 L sample of Freon gas initially at 50 mm Hg after its pressure is changed to

200 mm Hg at constant T?

Initial conditions Final conditions

P1 = 50 mm Hg P2= 200

mm Hg

V1 = 1.6 L V2 = ?

V2 = 1.6 L x 50 mm Hg = 0.4 L

200 mm Hg

Freon-12, (CCl2F2), is used in refrigeration systems. What is the new volume (L) of a

1.6 L sample of Freon gas initially at 50 mm Hg after its pressure is changed to

200 mm Hg at constant T?

Initial conditions Final conditions

P1 = 50 mm Hg P2= 200

mm Hg

V1 = 1.6 L V2 = ?

V2 = 1.6 L x 50 mm Hg = 0.4 L

200 mm Hg

The LAWS Charles’ law: In a fixed

amount of gas the Temperature of the gas is directly proportional to its volume when the pressure remains constant.

– Temperature & volume– As T then V– At constant P, n

Charles’ law: In a fixed amount of gas the Temperature of the gas is directly proportional to its volume when the pressure remains constant.

– Temperature & volume– As T then V– At constant P, n

V1 = V2

T1 T2

V1 = V2

T1 T2

Gay-Lussac’s law: In a fixed amount of gas the Temperature of the gas is directly proportional to its Presure when the volume remains constant.•Temperature & pressure•As P then T•At constant V, n

Gay-Lussac’s law: In a fixed amount of gas the Temperature of the gas is directly proportional to its Presure when the volume remains constant.•Temperature & pressure•As P then T•At constant V, n

P1 = P2

T1 T2

P1 = P2

T1 T2

The LAWSThe LAWS

Combined gas lawCombined gas law

PV=k1PV=k1 V/T=k2V/T=k2 P/T=k3P/T=k3

If we combine all of the relationships from the 3 laws covered thus far (Boyle’s, Charles’s, and Gay-Lussac’s) we can develop a mathematical equation that can solve for a situation where 3 variables change :

If we combine all of the relationships from the 3 laws covered thus far (Boyle’s, Charles’s, and Gay-Lussac’s) we can develop a mathematical equation that can solve for a situation where 3 variables change :

Combined gas lawCombined gas law Amount is held constant Is used when you have a

change in volume, pressure, or temperature

Amount is held constant Is used when you have a

change in volume, pressure, or temperature

P1V1T2 = P2V2T1P1V1T2 = P2V2T1

P1V1P1V1

T1T1

= = P2V2P2V2

T2T2