Gas: Definition, Properties, Examples

A gas is a form of matter characterized by its lack of a definite shape and volume. Gases exhibit lower density compared to solids and liquids, and their particles possess substantial kinetic energy while displaying minimal attraction to each other. The presence of significant empty space between particles allows gases to diffuse, spreading out uniformly within the container. As one of the three fundamental states of matter, gases display unique properties distinct from those of liquids and solids.

Gas- Definition

A gas is a state of matter characterized by particles that lack both a definite volume and shape. It is one of the fundamental states of matter, alongside solids, liquids, and plasma. Positioned between the liquid and plasma states under ordinary conditions, gases can be composed of single-element atoms (e.g., H₂, Ar), compounds (e.g., HCl, CO₂), or mixtures (e.g., air, natural gas). In the gaseous state, particles exhibit significant kinetic energy, resulting in wide spatial distribution and a lack of specific arrangement.

Gases, as substances in the gaseous state, represent one of the three fundamental states of matter. They possess notable compressibility and maintain considerable intermolecular distances. The gaseous state is characterized by weak interparticle forces, leading to substantial particle separation compared to liquids and solids. Notably, gases lack a definite volume or shape, displaying the ability to fill the entire container they occupy. Furthermore, gases are highly compressible and exert measurable pressure on the container walls.

Characteristics of Gases

Lower Density and High Compressibility:

• Gases exhibit a reduced density in comparison to solids and liquids.
• They possess high compressibility, allowing them to be squeezed into smaller volumes under pressure.

Uniform Pressure in All Directions:

• Gases exert pressure equally in all directions.
• This characteristic is a result of the constant and random motion of gas particles.

Significant Particle Spacing and High Kinetic Energy:

• Gas particles are widely spaced, creating a considerable amount of empty space between them.
• These particles possess high kinetic energy due to their rapid motion.

Negligible Intermolecular Forces:

• The forces between gas particles are minimal.
• Unlike solids and liquids, gases lack strong attractive forces, allowing for greater particle mobility.

High-Speed Particle Movement and Collisions:

• Gas particles move rapidly in various directions.
• Their high speeds lead to collisions among particles, contributing to the even distribution of gas within a container.

Container Conformation:

• Gases adapt to the volume and shape of the container they occupy.
• This property is a result of the continuous and random motion of gas particles, allowing them to fill the available space uniformly.

Examples of Gases

Industrial Gases:

• Acetylene
• Air
• Argon
• Carbon Dioxide
• Carbon Monoxide
• Helium
• Natural Gas
• Propane

Noble Gases:

• Helium (He)
• Neon (Ne)
• Argon (Ar)
• Krypton (Kr)
• Xenon (Xe)
• Radon (Rn)

Diatomic and Triatomic Gases:

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Ozone (O₃)
• Fluorine (F₂)
• Chlorine (Cl₂)

Kinetic Theory of Gases

The kinetic theory of gases serves as a crucial framework that connects the microscopic behavior of atoms and molecules within gases to their measurable macroscopic properties. Gases provide difficulties because they lack a distinct size and shape, in contrast to solids and liquids, which can be identified by physical characteristics like size and shape. By enabling us to characterize gas qualities using quantifiable macroscopic parameters—namely, pressure, volume, and temperature within the container—the kinetic theory proves essential in helping us overcome these obstacles.

In order to use the kinetic theory, gases must be thought of as collections of submicroscopic particles, such as atoms and molecules. This theory proposes that the pressure exerted by a gas arises from the constant collisions between these particles and the walls of the container. Beyond pressure, the kinetic theory extends its application to defining other critical properties, including temperature, volume, pressure, and transport properties like viscosity, thermal conductivity, and mass diffusivity. It essentially provides a comprehensive understanding of properties linked to the microscopic behavior of gas particles.

The kinetic theory is important because it makes a meaningful connection between the behaviors of microscopic organisms and the observations made at the macroscopic level. In other words, it helps to simplify the complex behaviors of gas molecules. Constantly in motion, gaseous molecules clash with the walls of the container as well as one another. The model also provides insights into related processes like Brownian motion. In essence, the kinetic theory of gases is an important theory for understanding the relationship between gas macroscopic behavior and the underlying microscopic dynamics.

Kinetic Theory of Gases Assumptions

• Gases consist of different molecules, each considered a rigid, elastic sphere and identical within the same gas.
• The size of gas molecules is extremely small compared to the distances between them.
• Gas molecules are in continuous random motion, exhibiting movement in all possible directions.
• Collisions occur between gas molecules and with surfaces, and these collisions are perfectly elastic.
• Molecules do not experience attractive or repulsive forces between collisions, maintaining independence.
• Molecular motion follows linear trajectories between collisions.
• Collisions are instantaneous, with negligible time duration for any given collision event.
• Despite molecular motion and collisions, the density of the gas remains uniform throughout its volume.

Real Gas and Ideal Gas

Ideal Gas: An ideal gas is like a perfect model that follows gas rules perfectly, especially at various temperatures and pressures. Even though no real gas is exactly like this ideal, some gases come really close under certain conditions. The idea of an ideal gas is based on a few assumptions. It pictures gas particles as solid, spherical objects with no attraction or repulsion between them. These particles move randomly in straight lines until they hit something, and when they do, they bounce off perfectly, keeping their energy. The assumption also includes the idea that the particles are tiny compared to the space between them, ensuring their average energy stays the same.

Real Gas: Any gas that exhibits real-world deviations from ideal behavior because of the fundamental characteristics of matter is considered a genuine gas. Real gases, as opposed to ideal gases, have non-negligible volumes in their particles and entail forces of attraction or repulsion between them. Extreme circumstances, like high pressure or low temperature, have a significant impact on the significance of particle size in actual gases. As a result, real gases exhibit departures from ideal behavior, which reflects the finite nature of particles in reality. Notwithstanding these variations, real gases can, under some circumstances, behave almost perfectly, offering a useful insight on the intricacies of gas behavior.

References

• https://byjus.com/chemistry/gas/
• https://www.techtarget.com/whatis/definition/gas
• https://www.britannica.com/science/gas-state-of-matter/Behaviour-and-properties
• https://byjus.com/jee/kinetic-theory-of-gases/
• https://www.studysmarter.co.uk/explanations/chemistry/physical-chemistry/ideal-and-real-gases/#: