There are four possible states of matter i.e., solid, liquid, gas and plasma. The simplest form of matter is the gaseous state and most of the matter around us in the solid state.so, matter can be defined as:
anything in the universe that has mass and occupies space is known as matter. matter consists of very small particles known as atoms or molecules.
matter exists in three common states: the fourth state is rare, is called plasma.
A state of matter that has no definite shape as well as no definite volume is called gas: it occupied all the space container which it is kept.
A state of matter that has a definite volume but no definite shape is called liquid. it occupies or attains the shape of the container in which it is kept.
A state of matter that has both definite shape and volume is called solid.
Liquids are less common than solids, gases, and plasmas. The reason is that the liquid state of any substance can exist only within a relatively narrow range of temperature and pressure.
the same substance may exist in three states. for example, water in the form of ice is solid; in the form of steam is gas, while a usual form of water is liquid.
it is the inter-molecular distances or spaces between the molecules, which makes difference among the three states. in solids, the molecules are closely packed with one another and have minimum inter-molecular distance. in gases, the molecules are free from one another and have very large inter-molecular distance. in liquids the situation is intermediate. they have large inter-molecular distance as compared to solids but much less than gases.
inter-molecular distance depends upon the following two opposing factors:
- inter-molecular attraction
- kinetic energy
Let us look at the general properties of gases, liquids and solids. Kinetic molecular theory of gases can help us understand their properties.
Properties of gases
- Gasses don`t have a definite volume and occupy all the available space. The volume of a gas is the volume of the container.
- They don`t have a definite shape and take the shape of the container just like liquids.
- Due to low densities of gases, as compared to those of liquids and solids, the gases bubble through liquids and tend to rise up.
- Gases can diffuse and effuse. This property is negligible in solids but operates in liquids as well.
- Gases can be compared by applying a pressure because there is largely empty space between their molecules.
- Gases can expand on heating or by increasing the available volume. Liquids and solids, on the other hand, do not show an appreciable increase in volume when they are heated.
- When the sudden expansion of gases occurs, it is called Joule Thomson effect.
- Molecules of gases are in a constant state of random motion. They can exert a certain pressure on the walls of the container and this pressure is due to the number of collisions.
- The intermolecular forces in gases are very weak.
Properties of liquids
- Liquids don`t have a definite shape but have a definite volume. Unlike solids, they adopt the shape of the container.
- Molecules of liquids are in a constant state of motion. The evaporation and diffusion of liquid molecules are due to this motion.
- The densities of liquids are much greater than those of gases but are close to those of solids.
- The space among the molecules of liquids is negligible just like solids.
- The intermolecular attractive forces in liquids are intermediate between gases and solids. The melting points and boiling points of gases, liquids, and solids depend upon the strength of such forces.
- Molecules of liquids possess kinetic energy due to their motion. Liquids can be converted into solids on cooling i.e., by increasing their kinetic energy. Molecules of liquids collide among themselves and exchange energy but those of liquids cannot do so.
Properties of solids
- The particles present in solid substances are very close to each other and they are tightly packed. Due to this reason, solids are non-compressible and they cannot diffuse into each other.
- There are strong attractive forces in solids which hold the particles together firmly and for this reason solids have definite shape and volume.
- The solid particles possess only vibrational motion.
Unit of pressure
The pressure of air that can support 760 mmHg column at sea level, is called one atmosphere. It is the force exerted by 760 mm or 76 cm long column of mercury on an area of 1cm2 at 0˚C. It is the average pressure of the atmosphere at sea level 1mmHg = 1 Torr. The S.I. unit of pressure is Nm-2 . one atmospheric pressure i.e. 760 torrs is equal to 101325 Nm-2.
1 pascal = 1Nm-2. Sp, 760torr = 101325Pa= 101.325 kilopascals (Kpa is another unit of pressure)
The unit pounds per square inch ( psi) is used most commonly in engineering work, and 1 atm =760 torr = 14.7 pounds inch-2 . the unit millibar is commonly used by meteorologists.