Question

What do you mean by the change of state of matter ? Explain :
(a) The change of a solid into a liquid at a constant temperature ,and
(b) the change of a liquid into a gas at a constant temperature .

Answer 1

A state of matter is one of the several forms that matter may take in physics. In everyday life, four states of matter are visible: solid, liquid, gas, and plasma. Many intermediate states, such as liquid crystal, are known to exist, while certain states, such as Bose–Einstein condensates, neutron-degenerate matter, and quark–gluon plasma, are known to exist only under severe circumstances, such as extreme cold, extreme density, and extreme energy.

Complete answer:
A substance's state of matter changes from solid to liquid or from liquid to gas when heat energy is applied at a constant temperature.

(a) Melting or fusing is the process of a substance changing from a solid to a liquid form after absorbing heat at a specific temperature, known as the melting point. Melting, also known as fusion, is a physical process that causes a substance's phase shift from solid to liquid. When the internal energy of a solid increases, usually due to the application of heat or pressure, the temperature of the substance rises to the melting point. The ordering of ions or molecules in a solid breaks down to a less ordered state at the melting point, and the solid "melts" to become a liquid.

(b) Boiling or evaporation is the process of a material changing from a liquid to a gaseous form at a specific temperature, known as the boiling point. Boiling is the fast evaporation of a liquid that occurs when it is heated to its boiling point, which is the temperature at which the liquid's vapour pressure equals the surrounding atmosphere's pressure. Water's boiling point is 100 degrees Celsius (212 degrees Fahrenheit) at sea level, but it lowers as height rises, corresponding to lower air pressures.

Note: All the molecules in a liquid do not have the same kinetic energy at any given temperature. Some high-energy particles on the liquid surface may have enough energy to break out from the liquid's intermolecular forces of attraction and form a gas. This is referred to as evaporation. Evaporation occurs just on the top of the liquid, whereas boiling occurs throughout the liquid. When a liquid reaches its boiling point, it produces gas bubbles that rise to the surface and then burst into the air. Boiling is the term for this procedure. The temperature of a boiling liquid does not grow when the temperature is increased, rather the liquid boils faster.