BackChapter 8: Gases – Properties and Behavior (General Chemistry Study Notes)
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Gases: Properties and Behavior
Kinetic Molecular Theory
The Kinetic Molecular Theory explains the behavior of gases at the molecular level. It is based on several key assumptions about the nature of gas particles:
Gas particles are small and move rapidly in straight lines.
They experience essentially no attractive or repulsive forces between each other.
Gas particles are very far apart relative to their own size.
The actual volume of the gas particles is negligible compared to the volume of the container they occupy.
The kinetic energy of gas particles increases as temperature increases.
Example: The random, rapid movement of air molecules in a room is a direct result of these principles.
Properties That Describe a Gas
Gases are described using four fundamental properties: pressure (P), volume (V), temperature (T), and amount (n). Each property is measurable and interrelated with the others.
Property | Description | Units of Measurement |
|---|---|---|
Pressure (P) | The force exerted by a gas against the walls of the container | atmosphere (atm); millimeter of mercury (mmHg); torr (Torr); pascal (Pa) |
Volume (V) | The space occupied by a gas | liter (L); milliliter (mL) |
Temperature (T) | The determining factor of the kinetic energy of gas particles | degree Celsius (°C); kelvin (K) is required in calculations |
Amount (n) | The quantity of gas present in a container | gram (g); mole (mol) is required in calculations |
Volume
The volume of a gas is defined as the space it occupies, which is the same as the volume of its container. Volume is typically measured in liters (L) or milliliters (mL). At constant pressure, the volume of a gas increases as temperature increases.
Example: A balloon expands when heated because the gas inside increases in volume.
Temperature
The temperature of a gas is directly related to the average kinetic energy of its molecules. It is measured in Kelvin (K) for all gas law calculations.
When temperature decreases, gas molecules have fewer collisions (lower kinetic energy).
When temperature increases, gas molecules have more collisions (higher kinetic energy).
Conversion: To convert from Celsius to Kelvin:
Pressure
Pressure is the result of gas particles colliding with the walls of their container. It is measured in several units:
Millimeters of mercury (mmHg) or Torr
Atmospheres (atm)
Pascals (Pa) or kilopascals (kPa)
Pounds per square inch (psi)
Standard pressure conversions:
Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere. It decreases as altitude increases and is 1 atm at sea level.
Example: At higher elevations, atmospheric pressure is lower than at sea level.
Summary Table: Units for Measuring Pressure
Unit | Abbreviation | Equivalent to 1 atm |
|---|---|---|
Atmosphere | atm | 1 atm |
Millimeter of mercury | mmHg | 760 mmHg |
Torr | Torr | 760 Torr |
Pounds per square inch | psi | 14.7 psi |
Pascals | Pa | 101,325 Pa |
Kilopascals | kPa | 101.325 kPa |
Additional info: These foundational concepts are essential for understanding the behavior of gases and for applying the gas laws in quantitative problems.
