16-07-2012, 02:59 PM
DALTON’S LAW OF PARTIAL PRESSURE, AVOGADRO’S LAW, IDEAL GAS LAW
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DALTON’S LAW OF PARTIAL PRESSURE
In 1801, Dalton found out that the total pressure of a mixture of gases is equal to the sum of the partial pressure exerted by each gas. This is known as Dalton’s law of partial pressure.
Each gas in the mixture exerts a pressure that is independent of the other gases present. These pressures are called partial pressures.
Dalton’s Law of Partial Pressure can be explained by 2 concepts from the Kinetic Molecular Theory.
The pressure of a gas is caused by the collision of molecules with the walls of the container.
Gas molecules act independently of each other.
DALTON’S LAW OF PARTIAL PRESSURE: APPLICATION
Gas exchange between living organisms and the environment depends on the properties of gases, in particular, partial pressure and solubility.
RESPIRATION is one of the most important processes because we need to breathe OXYGEN and breathe out CO2 in order to live.
Oxygen is the most important gas in the atmosphere, it makes up 21 % of the volume of dry air.
Partial pressure of a gas is more useful than percentage composition because it is the pressure of oxygen that determines how much oxygen is absorbed by the lungs of the person.
21 % of the volume and pressure of the atmosphere is due to OXYGEN. The partial pressure of oxygen can be calculated by multiplying the percent in decimal form by the total pressure.
POXYGEN = 0.21 X 760 torr = 159.6 torr
We function best breathing this partial pressure of oxygen.
DID YOU KNOW
You may have about 3.5 x 102 tiny ALVEOLI (air sacs) in each lung. The surface area of contact with capillaries for absorbing oxygen is about 75 m2, about four (4) times as much area as an average classroom floor!
When we live at higher elevations, the partial pressure of oxygen is lower and our bodies adjust accordingly.
On top of the highest mountain, e.g. MT. EVEREST, the total atmospheric pressure is 270 torr, so the partial pressure of oxygen is only 56.7 torr, or about 1/3 of normal.
POXYGEN = 0.21 X 270 torr = 56.7 torr
A human being cannot survive for long at such a low pressure of oxygen.
At that altitude, even conditioned climbers must use an oxygen tank and mask, which give an increased partial pressure of oxygen to the lungs.
DALTON’S LAW OF PARTIAL PRESSURE: TOTAL PRESSURE
SAMPLE EXERCISES
An equilibrium mixture contains H2 at 560 torr, N2 at 180 torr and O2 at 250 torr pressure. What is the total pressure of the gases, in mm Hg and atm, in the system?
SAMPLE EXERCISES
2. In a compressed air tank for scuba diving to a depth of 30 m, a mixture with an oxygen partial pressure of 28 atm and a nitrogen partial pressure of 110 atm is used. What is the total pressure in the tank?
SAMPLE EXERCISES
3. The total pressure of a gas mixture in a cylinder is 6.40 atm. Gas A exerts a pressure three times that of gas B. Gas C exerts a pressure twice that of gas A. What will be the pressure of gas A, B, C if they occupy the cylinder alone?
DALTON’S LAW OF PARTIAL PRESSURE: WATER DISPLACEMENT METHOD
Another application of partial pressures is THE COLLECTION OF GAS BY THE DISPLACEMENT OF WATER.
Hydrogen and oxygen are often generated in the lab and collected by bubbling the gases into a container filled with water. Both of this gases have a relatively low solubility in water.
However, water evaporates relatively easily and the gas collected will be mixed with some water vapor.
Water vapor is a gas like any other gas and the pressure exerted by a gas above its liquid is called VAPOR PRESSURE.
The vapor pressure of water at different temperature is well known. See Table 13.2 , p. 253 of your textbook.
Dalton’s law of partial pressures and a table of known vapor pressures of water can be used to determine the pressure of dry gas that has been collected.
SAMPLE PROBLEM
In a laboratory, oxygen gas was collected by water displacement at an atmospheric pressure of 726 torr and a temperature of 22°C. Calculate the partial pressure of dry oxygen.
SOLUTION to Sample Problem
PTOTAL = 726 torr
PWATER= 19.8 torr (22 °C)
POXYGEN = ?
PTOTAL = POXYGEN + PWATER
POXYGEN = PTOTAL – PWATER
= 726 torr – 19.8 torr
POXYGEN = 706.2 torr
[attachment=27749]
DALTON’S LAW OF PARTIAL PRESSURE
In 1801, Dalton found out that the total pressure of a mixture of gases is equal to the sum of the partial pressure exerted by each gas. This is known as Dalton’s law of partial pressure.
Each gas in the mixture exerts a pressure that is independent of the other gases present. These pressures are called partial pressures.
Dalton’s Law of Partial Pressure can be explained by 2 concepts from the Kinetic Molecular Theory.
The pressure of a gas is caused by the collision of molecules with the walls of the container.
Gas molecules act independently of each other.
DALTON’S LAW OF PARTIAL PRESSURE: APPLICATION
Gas exchange between living organisms and the environment depends on the properties of gases, in particular, partial pressure and solubility.
RESPIRATION is one of the most important processes because we need to breathe OXYGEN and breathe out CO2 in order to live.
Oxygen is the most important gas in the atmosphere, it makes up 21 % of the volume of dry air.
Partial pressure of a gas is more useful than percentage composition because it is the pressure of oxygen that determines how much oxygen is absorbed by the lungs of the person.
21 % of the volume and pressure of the atmosphere is due to OXYGEN. The partial pressure of oxygen can be calculated by multiplying the percent in decimal form by the total pressure.
POXYGEN = 0.21 X 760 torr = 159.6 torr
We function best breathing this partial pressure of oxygen.
DID YOU KNOW
You may have about 3.5 x 102 tiny ALVEOLI (air sacs) in each lung. The surface area of contact with capillaries for absorbing oxygen is about 75 m2, about four (4) times as much area as an average classroom floor!
When we live at higher elevations, the partial pressure of oxygen is lower and our bodies adjust accordingly.
On top of the highest mountain, e.g. MT. EVEREST, the total atmospheric pressure is 270 torr, so the partial pressure of oxygen is only 56.7 torr, or about 1/3 of normal.
POXYGEN = 0.21 X 270 torr = 56.7 torr
A human being cannot survive for long at such a low pressure of oxygen.
At that altitude, even conditioned climbers must use an oxygen tank and mask, which give an increased partial pressure of oxygen to the lungs.
DALTON’S LAW OF PARTIAL PRESSURE: TOTAL PRESSURE
SAMPLE EXERCISES
An equilibrium mixture contains H2 at 560 torr, N2 at 180 torr and O2 at 250 torr pressure. What is the total pressure of the gases, in mm Hg and atm, in the system?
SAMPLE EXERCISES
2. In a compressed air tank for scuba diving to a depth of 30 m, a mixture with an oxygen partial pressure of 28 atm and a nitrogen partial pressure of 110 atm is used. What is the total pressure in the tank?
SAMPLE EXERCISES
3. The total pressure of a gas mixture in a cylinder is 6.40 atm. Gas A exerts a pressure three times that of gas B. Gas C exerts a pressure twice that of gas A. What will be the pressure of gas A, B, C if they occupy the cylinder alone?
DALTON’S LAW OF PARTIAL PRESSURE: WATER DISPLACEMENT METHOD
Another application of partial pressures is THE COLLECTION OF GAS BY THE DISPLACEMENT OF WATER.
Hydrogen and oxygen are often generated in the lab and collected by bubbling the gases into a container filled with water. Both of this gases have a relatively low solubility in water.
However, water evaporates relatively easily and the gas collected will be mixed with some water vapor.
Water vapor is a gas like any other gas and the pressure exerted by a gas above its liquid is called VAPOR PRESSURE.
The vapor pressure of water at different temperature is well known. See Table 13.2 , p. 253 of your textbook.
Dalton’s law of partial pressures and a table of known vapor pressures of water can be used to determine the pressure of dry gas that has been collected.
SAMPLE PROBLEM
In a laboratory, oxygen gas was collected by water displacement at an atmospheric pressure of 726 torr and a temperature of 22°C. Calculate the partial pressure of dry oxygen.
SOLUTION to Sample Problem
PTOTAL = 726 torr
PWATER= 19.8 torr (22 °C)
POXYGEN = ?
PTOTAL = POXYGEN + PWATER
POXYGEN = PTOTAL – PWATER
= 726 torr – 19.8 torr
POXYGEN = 706.2 torr