GASEOUS STATE OF MATTERS

 Introduction 

Everything in the universe has a chemical identity. We know that the smallest particle of matter is an atom. “Study of matter and the changes that it undergoes” can simply be understood as the basic definition of chemistry. Usually matter is anything that occupies space and has mass and can be seen and touched (such as soil, water) as well as things we cannot see such as air. Based on the composition and properties, several categories such as substances, mixtures, elements as well as atoms and molecules can be identified. All substances, at least in principle, can exist in three states: solid, liquid and gas. In a solid, particles are held tightly and close together in an ordered structure with a definite shape having a small degree of motion. Particles in a liquid are close together but are not held so tightly in position and can move faster compared to that of solid. Gases differ largely from liquids and solids in the distances between the particles. In a gas, the particles are separated by distances, large compared with the size of the particles allowing them to behave freely. Therefore, the attractive forces between gas particles are very small or negligible and that allows us to consider gas particles individually and some hypotheses are easily predictable depending on the temperature and pressure changes.

Behaviour of particles and their characteristics in solids ,liquid and gases.

Anything that occupies space and has a mass can be called “matter”. This could be things we can see and touch like trees or things we cannot see like the air we breathe. All matter can be classified broadly into three states solid, liquid and gas. Matter can be interconverted among these three states without changing the composition. For an example water in liquid state can be converted to gaseous state (steam) when heated and can be converted to a solid (ice) if cooled.

Three states of matter differ based on arrangement and movement of particles. The inter-particle distance is highest in gaseous state and lowest in solids. In liquid state, particles are relatively closer compared to gaseous state, yet not too close compared to the solid state. Therefore, a regular pattern of particles can be seen only in solid state, while both gaseous and liquid state particles show random arrangement. As a result, particles in gaseous state can move fast and freely compared to liquid state particles. However, movement of particles in solids is limited to vibrations. The arrangement and motions of particles in matter result in differences in macroscopic properties such as volume, shape, compressibility and density as indicated in the Table below👇

Note: Here we say that a liquid takes the shape of the container and we have to thinkwhy we get these shapes. Usually, particles of any object is being pulled by a variety of forces such as intermolecular forces, and that’s why it has shape. Some given amount (volume) of water in a beaker is being shaped by surface tension resulting from intermolecular forces within the liquid creating a meniscus curve at the edge of the surface, by the force of the walls of the beaker pushing up on it, and by the gravity which is greater than the surface tension, pulling it down. So, it takes the shape of the beaker, with a flat surface on the top. This happens due to the satisfaction of all those different forces. However, in the case that the surface tension is stronger than gravity, the water’s surface might not lie flat by taking the shape of the container. Assume that there is no gravity, and so surface tension is very much high. As each part of the surface wants to stay as close as possible to the rest of the surface it tries to minimize the forces within. So,the shape that best allows this is a sphere, because it is the shape that has the minimal surface area for a given volume.

Matter in one particular state can be converted to another state by heating or cooling. Increase of temperature makes particles move faster and inter-particle distance becomes greater leading to change in state. Accordingly, increase in temperature converts solid state materials to liquid and liquid state materials to gaseous state. The opposite happens with decreasing temperature. Figure illustrates how matter can be interconverted among states.

As an example for above process.Let, take water as example ,

When we describe the properties of the three states of matter with the help of Table(see the comparisontable),motion and arrangement of particles are basically considered. Especially, thermal energy is the energy of a body arising from motion of its atoms or molecules and it is directly proportional to the temperature of the substance. Therefore, it measures the average kinetic energy of the particles of the matter and is thus responsible for movement of particles or the thermal motion.

As we already know, interparticle forces tend to keep the particles together but thermal energy of the particles tends to keep them apart. Therefore the existence of three states of matter can be regarded as a result of balance between interparticle forces and the thermal energy of the particles.When inter molecular interactions are very weak, molecules do not tend to make liquid or solid unless thermal energy is reduced by lowering the temperature. Gases do not liquefy on compression only, although molecules come very close to each other andintermolecular forces operate to the maximum. However, when thermal energy of molecules is reduced by lowering the temperature, the gases can very easily be liquefied.These behaviours can be explained by Figure (see the above figure)where we can understand the reversible nature of intermolecular forces and the thermal energy acting on the three states of matter.

GASEOUS STATE OF MATTERS 

Let us now focus our attention on the behaviour of substances which exist in the gaseous state under normal conditions of temperature and pressure. 

The gaseous state is characterized by the following physical properties as described in Table above.

👊 Gases are highly compressible.

👊 Gases exert pressure equally in all directions.

👊 Gases have much lower density than the solids and liquids.

👊The volume and the shape of gases are not fixed. These assume volume and shape of the container.

👊Gases mix evenly and completely in all proportions without any mechanical aid.

Simplicity of gas is due to the fact that the forces between their molecules are negligible.Their behaviour is governed by same general laws (will be discussed later), which were discovered as a result of experimental studies. These laws are usually relationships between measurable properties of gases. Some of these properties like pressure, volume, temperature and amount (moles or mass) are very important because relationships between these variables describe state of the gas.

Interdependence of these variables leads to the formulation of gas laws.

Made With reference of 

Chemistry Resource Book - Physical Chemistry -Part I