Post on 31-Dec-2015
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What is Pressure?
P= Force/area
Pressure units are N/m2 or Pascal(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 a result of the fact that air has mass and is attracted by gravity producing a force.
• Air pressure can vary daily.
One Square inch of atmosphere
weighs
14.7lbs14.7lbs..
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
Pressure
Standard Temperature = 0°C or 273KStandard Pressure = 1atm or 760mmHg or
101.3kPa (Units depend upon the method of
measure)
Why is a mmHg called a Why is a mmHg called a TorrTorr??
Evangelista Torricelli was born in Italy in 1608. Due to the great Italian, Galileo’s suggestion, Torricelli 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.
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…
What does the invention of the Barometer mean?
That ….
NOTHING SUCKS!
HUH?...You do not
SUCK on a straw.
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 SucksSucks what happens?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.
Low
Press
ure
High atmospheric Pressure
Mouth must
make a se
al
Pressure
Pressure always pushes pushes from high pressure to low pressure.
We measure the amount of push using either an open or closed manometer
A closed manometer is the same as Torricelli’s barometer.
One atmosphere = 760 mm of Hg = 101 kPa So 1.00 mm of Hg = 0.133 kPA
Dalton’s Law The pressure exerted by each gas in an unreactive mixture is
independent of the pressure exerted by other gases.
The pressure of each gas in a mixture is called the partial pressure of that gas.
Dalton’s law of partial pressures states that the total pressure of a gas mixture is the sum of the partial pressures of the component gases.
The Formula
Ptotal = P1+P2+P3 +…
Dalton’s Law of Partial PressureDalton’s Law of Partial Pressure
PT=P1+P2+P3+…PT=P1+P2+P3+…
John DaltonJohn Dalton1766-18441766-1844
Three of the primary components of air are CO2, N2, and O2. In a sample containing a mixture of these gases at exactly 760 mmHg, the partial pressures of CO2 and N2 are given as PCO2
= 0.285mmHg
PN2 = 593.525mmHg.
What is the partial pressure of O2?
Three of the primary components of air are CO2, N2, and O2. In a sample containing a mixture of these gases at exactly 760 mmHg, the partial pressures of CO2 and N2 are given as PCO2
= 0.285mmHg
PN2 = 593.525mmHg.
What is the partial pressure of O2?
Simple Dalton’s Law Calculation
Simple Dalton’s Law Calculation
PT = PCO2 + PN2 + PO2PT = PCO2 + PN2 + PO2
Simple Dalton’s Law Calculation
Simple Dalton’s Law Calculation
760mmHg = .285mmHg + 593.525mmHg + PO2
760mmHg = .285mmHg + 593.525mmHg + PO2
PO2= 167mmHgPO2= 167mmHg
• Partial Pressures are also important when a gas is “collected over water.”—Any time a gas is collected through
water the gas is “contaminated” with water vapor.
—You can determine the pressure of the dry gas by subtracting out the water vapor
• Partial Pressures are also important when a gas is “collected over water.”—Any time a gas is collected through
water the gas is “contaminated” with water vapor.
—You can determine the pressure of the dry gas by subtracting out the water vapor
Dalton’s Law of Partial PressureDalton’s Law of Partial Pressure
Ptot = Patmospheric pressure = Pgas + PH2OPtot = Patmospheric pressure = Pgas + PH2O
AtmosphericPressure
AtmosphericPressure
—The water’s vapor pressure can be determined from a list and subtract-ed from the atmospheric pressure
—The water’s vapor pressure can be determined from a list and subtract-ed from the atmospheric pressure
WATER VAPOR PRESSURESWATER VAPOR PRESSURES
Temp (°C) Vapor pressure (kPa)
11 0.651760.65176
55 .87260.87260
1010 1.22811.2281
1515 1.70561.7056
2020 2.33882.3388
2525 3.16913.1691
3030 4.24554.2455
3535 5.62675.6267
4040 7.38147.3814
4545 9.58989.5898
5050 12.34412.344
WATER VAPOR PRESSURESWATER VAPOR PRESSURES
Temp (°C) Vapor pressure (kPa)
5555 15.75215.752
6060 .19.932.19.932
6565 25.02225.022
7070 31.17631.176
7575 38.56338.563
8080 47.37347.373
8585 57.81557.815
9090 70.11770.117
9595 84.52984.529
100100 101.32101.32
105105 120.79120.79
Determine the partial pressure of oxygen collected by water displacement if the water temperature is 20.0°C and the total pressure of the gases in the collection bottle is 730.0 mmHg.
Determine the partial pressure of oxygen collected by water displacement if the water temperature is 20.0°C and the total pressure of the gases in the collection bottle is 730.0 mmHg.
Dalton’s Law CalculationDalton’s Law Calculation
PH2O at 20.0°C= 2.3388 kPaPH2O at 20.0°C= 2.3388 kPa
We need to convert to mmHg.We need to convert to mmHg.
PT = PH2O + PO2PT = PH2O + PO2
Dalton’s Law CalculationDalton’s Law Calculation
730.0 mmHg = 17.5468 + PO2730.0 mmHg = 17.5468 + PO2
PO2= 712.5 mmHgPO2= 712.5 mmHg
PH2O = 17.5468 mmHgPH2O = 17.5468 mmHg
2.3388 kPa 760 mmHg= 17.5468
mmHg1 101.3 kPa