Common States Of Matter

Matter is anything that has mass and occupies space. There are three common states of matter i.e. solid, liquid and gas. Solid has definite shape as well as definite volume. Liquid has a definite volume but not definite shape and it takes the shape of vessel in which it is kept. Gas has neither definite shape nor definite volume, it takes the shape of vessel in which it is kept and occupies all the space available to it.

6.1.1. Kinetic Description of States of Matter

According to kinetic molecular theory, matter is composed of very tiny particles, which are called as molecules. These molecules are always in motion and they possess kinetic energy. The three states of matter depend upon the arrangements, motions and forces of attraction between these particles. The difference between solid, liquid and gas is explained as follows:

Solid State: In solid state molecules or particles are tightly packed with one another and they have only back and forth motion (Vibrational motion) about their fixed positions. Therefore particles in solid cannot slip or slide over one another and thus they possess definite shape and definite volume.

Liquid State: In liquid state molecules are not tightly packed with one another. Their positions are not fixed and they can move in all direction, hence liquid does not have any definite shape. But in liquid state the kinetic energy of molecules is less than gaseous state. Therefore intermolecular attractive forces are more than gaseous state. Due to these intermolecular attractive forces liquid has a fixed volume.

Gaseous State: In gaseous state molecules are lying away from one another and they can move in all direction easily. The cohesive forces in a gas are negligible and the particles are free to move about in all directions. The kinetic energy possessed by these molecules are very high, therefore gases have neither definite shape nor definite volume.

6.1.2 Inter Conversion of Three States

Most of the important properties of liquids, solids and gases depend upon the inter conversion of one state into another state. For example when ice is warmed, it melts into liquid state, water. When water is heated and boiled, it changes into vapour (gas) state; some solids upon heating instead of changing into liquid state are converted directly into gaseous (vapour) state. This process is called sublimation. The examples of such substances are iodine, ammonium chloride and napthaline. These chemical substances being in solid state, when heated are sublimed directly kV vapours state. In general, each state may be converted into another state is explained as given below:

When a solid is heated, then the kinetic energy of particles increases and it becomes hot. If heating is continued then at certain temperature, the added energy becomes enough to overcome the attractive forces holding particles of solid in their fixed positions and it starts melting. The temperature at which solid starts melting is called melting point. At this point solid particles lose their fixed positions as well as their arrangements and thus solid is converted into liquid. At melting point the temperature of solid and liquid remains same until all the solid is melted though heat. It means in this condition the rise in temperature is used in change of state from solid to liquid and this change is called fusion.

When liquid is heated, the kinetic energy of liquid molecules increases. Due to increase of kinetic energy certain molecules start escaping from the surface of liquid and this escape of molecules is called evaporation. At certain temperature the vapour pressure of liquid becomes equal to external pressure and at this temperature liquid starts boiling. This temperature is called boiling point. Actually boiling point is the temperature at which the vapour pressure of a liquid becomes equal to external pressure applied on the liquid. At this point bubbles of vapours are able to form within the interior of liquid and then rise to the surface, where they burst and release vapours and thus liquid is converted into gas. At boiling point the temperature of liquid remains same until all of the liquid is evaporated or vapourized though heat. It means in this condition the rise in temperature is used in the change of state from liquid to gas, and this change is called vapourization.

 

 
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