Chemistry Chapter 4: Gases

Chemistry Chapter 4: Gases

• Gases are substances with molecules that are far apart, having weak attractions compared to other states of matter.
• "Khaos" is a Greek word that gave rise to the term "gas," meaning emptiness or gap.
• Gas molecules move randomly in all directions, colliding with each other and container walls.
• Gases can be classified as monoatomic, diatomic, or polyatomic, based on elemental composition.
• Noble gases (Helium, Neon, Argon) are monoatomic, while oxygen and hydrogen are diatomic examples.
• Gases like methane and carbon dioxide are examples of polyatomic gases.
• Gases have various uses, such as in photosynthesis, vehicles, power plants, and kitchens.
• The Kinetic Molecular Theory (KMT) of gases describes the behavior of gas molecules.
• Gas molecules are in constant, random motion. The volume of gas particles is negligible.
• There are no attractive or repulsive forces between ideal gas molecules.
• Average kinetic energy is directly proportional to absolute temperature.
• Pressure is force applied per unit area, measured in Pascals (Pa), atmospheres (atm), kilopascals (kPa), or torr.
• 1 atm = 760 mmHg = 14.7 psi = 101325 Pa
• A barometer measures atmospheric pressure, and a manometer measures gas pressure.

Postulates of Kinetic Molecular Theory

• Molecules: Gases consist of tiny particles called molecules (e.g., monoatomic, diatomic, polyatomic).
• Volume: The actual volume of a gas is negligible compared to its container volume.
• Movement: Gas molecules are in continuous random motion, colliding with each other and the container walls.
• Mean Free Path: The average distance a gas molecule travels between collisions is its mean free path.
• Pressure: Gas molecules exert pressure on the container walls after collisions.
• Forces: There are no attractive or repulsive forces between ideal gas molecules.
• Energy: Average kinetic energy of gas molecules is directly proportional to absolute temperature.

Absolute Zero (Definition)

• The temperature at which the volume of an ideal gas becomes zero.

Boyle's Law

• At constant temperature, the volume of a gas is inversely proportional to its pressure.

Charles's Law

• At constant pressure, the volume of a gas is directly proportional to its absolute temperature.

Avogadro's Law

• At constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas.

Dalton's Law of Partial Pressures

• The total pressure of a mixture of non-reacting gases is the sum of the partial pressures of each gas.

Graham's Law of Diffusion and Effusion

• The rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass.

Liquefaction of Gases

• Converting a gas into a liquid by lowering the temperature or increasing pressure (or both).
• Linde's method uses the Joule-Thomson effect, allowing gases to cool under pressure as they expand.

Plasma (Fourth State of Matter)

• A state of matter consisting of positive ions, electrons, and neutral particles, having equal amounts of positive and negative charges.
• Found in stars, lightning, and fluorescent lights.
• Useful in various applications, including electronic devices, medical processes, industrial applications, and lighting.