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How Stuff Works: Popcorn
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Properties of Gases
Gases are easily expandable and compressible unlike solids and liquids. Gases have a measurement of pressure. Pressure is defined as force exerted per unit area of surface. It can be measured in several units such as kilopascals (kPa), atmospheres (atm), and millimeters of Mercury (mmHg). Gas has a low density because its molecules are spread apart over a large volume. A gas will fill whatever container that it is in. An example of this is a bottle of ammonia being opened in a room and the smell traveling throughout the room.
The Kinetic Molecular Theory is the basis of the many properties of gases. The five postulates to the Kinetic Theory are as follows:
The Kinetic Molecular Theory is the basis of the many properties of gases. The five postulates to the Kinetic Theory are as follows:
- Gases are composed of molecules whose size is negligible compared to the average distance between them.
- Molecules move randomly in straight lines in all directions and at various speeds.
- The forces of attraction or repulsion between two molecules in a gas are very weak or negligible, except when they collide.
- When molecules collide with one another, the collisions are elastic; no kinetic energy is lost.
- The average kinetic energy of a molecule is proportional to the absolute temperature.
- 1 atm
- 760 mmHg
- 76 cmHg
- 101.3 kPa
- 760 torr
Boyle's Law
Boyle's Law states the volume of a definite quantity of dry gas is inversely proportional to the pressure, provided the temperature remains constant.
Mathematically Boyle's law can be expressed as P1V1 = P2V2
Mathematically Boyle's law can be expressed as P1V1 = P2V2
- V1 is the original volume
- V2 is the new volume
- P1 is original pressure
- P2 is the new pressure
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Charles' Law
Charles's Law can be stated as the volume occupied by any sample of gas at a constant pressure is directly proportional to the absolute temperature.
V / T =constant
V is the volume
T is the absolute temperature (measured in Kelvin)
Charles's Law can be rearranged a more useful equation
V1 / T1 = V2 / T2
V1 is the initial volume
T1 is the initial temperature
V2 is the final volume
T2 is the final temperature
V / T =constant
V is the volume
T is the absolute temperature (measured in Kelvin)
Charles's Law can be rearranged a more useful equation
V1 / T1 = V2 / T2
V1 is the initial volume
T1 is the initial temperature
V2 is the final volume
T2 is the final temperature
charles_law.docx | |
File Size: | 107 kb |
File Type: | docx |
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STP and Collecting Gases Over Water
STP is Standard Temperature and Pressure. STP is O Celcius and 1 atmosphere of pressure (101.325kPa). Gases properties can be compared using STP as a reference.
To obtain the pressure of gas collected over water the partial pressure of the water must be taken into consideration. The reason for this is as the gas bubbles through the water the gas picks up water vapor. The amount of water vapor the gas picks up only depends on the temperature. To calculate the pressure of the gas the partial pressure of the water must be subtracted from the pressure in the container.
To obtain the pressure of gas collected over water the partial pressure of the water must be taken into consideration. The reason for this is as the gas bubbles through the water the gas picks up water vapor. The amount of water vapor the gas picks up only depends on the temperature. To calculate the pressure of the gas the partial pressure of the water must be subtracted from the pressure in the container.
Combined Gas Law
The combined gas law is a combination of Boyle's Law and Charles's Law; hence its name the combined gas law. In the combined gas law, the volume of gas is directly proportional to the absolute temperature and inversely proportional to the pressure.
This can be written as PV / T = constant. Since for a given amount of gas there is a constant then we can write P1V1 / T1 = P2V2 / T2.
This can be written as PV / T = constant. Since for a given amount of gas there is a constant then we can write P1V1 / T1 = P2V2 / T2.
- P1 is the initial pressure
- V1 is the initial volume
- T1 is the initial temperature (in Kelvin)
- P2 is the final pressure
- V2 is the final volume
- T2 is the final temperature (in Kelvin)
Avogadro's Hypothesis
Any gas, when measured at the same temperature and pressure will always contain the same number of gas particles.
avogadros_law.ppt | |
File Size: | 1032 kb |
File Type: | ppt |
Ideal Gas Law
The ideal gas law is a combination of all the gas laws. The ideal gas law can be expressed as PV = nRT.
- P is the pressure in kPa
- V is the volume in litres
- n is the number of moles
- R is a constant
- T is the temperature in Kelvin
molar_volume_gas.doc | |
File Size: | 64 kb |
File Type: | doc |
gas_laws_review_question.doc | |
File Size: | 31 kb |
File Type: | doc |