# The GAS LAWS Gases have mass Gases diffuse Gases expand to fill containers Gases exert pressure Gases are compressible Pressure & temperature are dependent.

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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 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 Variables

What is Pressure? Pressure is the amount of force per unit area. The Units of Pressure are N/m 2 or Pascals (Pa) Pressure is the amount of force per unit area. The Units of Pressure are N/m 2 or Pascals (Pa)

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.

What is atmospheric Pressure? Atmospheric pressure is the pressure created by the mass of the gas molecules in the air being pulled to the surface of the Earth. Atmospheric pressure is the pressure created by the mass of the gas molecules in the air being pulled to the surface of the Earth. Atmospheric pressure is caused by the mass of air that is pulled down by gravity. The weight of air creates a force. Atmospheric pressure is caused by the mass of air that is pulled down by gravity. The weight of air creates a force. Air pressure can vary Air pressure can vary Atmospheric pressure is the pressure created by the mass of the gas molecules in the air being pulled to the surface of the Earth. Atmospheric pressure is the pressure created by the mass of the gas molecules in the air being pulled to the surface of the Earth. Atmospheric pressure is caused by the mass of air that is pulled down by gravity. The weight of air creates a force. Atmospheric pressure is caused by the mass of air that is pulled down by gravity. The weight of air creates a force. Air pressure can vary Air pressure can vary One Square inch of atmosphere weighs14.7lbs.

How does that pressure feel? The behavior of a gas depends very strongly on the temperature and the pressure of the gas. STP. To make it easier to discuss the behavior of a gas, it is convenient to designate a set of standard conditions, called STP. Standard Temp and Standard Pressure Standard Temperature = 0°C or 273K Standard Temperature = 0°C or 273K Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa The behavior of a gas depends very strongly on the temperature and the pressure of the gas. STP. To make it easier to discuss the behavior of a gas, it is convenient to designate a set of standard conditions, called STP. Standard Temp and Standard Pressure Standard Temperature = 0°C or 273K Standard Temperature = 0°C or 273K Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa Standard Pressure =1.00 atm or 760 mmHg or 101.3kPa

Why is a mmHg called a Torr? inability Evangelista Torricelli was born in Italy in 1608. He investigated the phenomenon of the inability 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. inability Evangelista Torricelli was born in Italy in 1608. He investigated the phenomenon of the inability 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 1 st 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 1 st 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 doesnt SUCK! YOU dont even SUCK face when you Kiss!

So if nothing Sucks(Pulls) what happens? Everything ….. PUSHES!! Everything ….. PUSHES!!

Lets 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. Low Pressure High atmospheric Pressure Mouth must make a seal

Pressure pushes Pressure always pushes from high pressure to low pressure. We measure the amount of push using a closed manometer A closed manometer is the same as Torricellis barometer. pushes Pressure always pushes from high pressure to low pressure. We measure the amount of push using a closed manometer A closed manometer is the same as Torricellis barometer.

P 1 V 1 = P 2 V 2 Boyles 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 Boyles 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 LAWS

Boyles 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 Boyles Law Problem Freon-12, (CCl 2 F 2 ), 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 P 1 = 50 mm HgP 2 = 200 mm Hg V 1 = 1.6 LV 2 = ? V 2 = 1.6 L x 50 mm Hg = 0.4 L 200 mm Hg Freon-12, (CCl 2 F 2 ), 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 P 1 = 50 mm HgP 2 = 200 mm Hg V 1 = 1.6 LV 2 = ? V 2 = 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 V 1 = V 2 T 1 T 2 V 1 = V 2 T 1 T 2

Gay-Lussacs 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-Lussacs 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 P 1 = P 2 T 1 T 2 P 1 = P 2 T 1 T 2 The LAWS

Combined gas law PV = k 1 V/T = k 2 P/T = k 3 If we combine all of the relationships from the 3 laws covered thus far (Boyles, Charless, and Gay- Lussacs) we can develop a mathematical equation that can solve for a situation where 3 variables change :

Combined 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 P 1 V 1 T 2 = P 2 V 2 T 1 P1V1P1V1 P1V1P1V1 T1T1 T1T1 = = P2V2P2V2 P2V2P2V2 T2T2 T2T2

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