Question

How does matter change when it is heated or cooled?

Answer 1

Matter basically exists in three states i.e. solid, liquid and gas. The kinetic theory of matter can be used to explain how interconversion from one state to another can be achieved by heating or cooling the substance. If a substance is heated, heat is added to the system and if the substance is cooled , heat is removed from the system.

Complete step by step answer:
Step 1: When matter is heated:
Case 1: Solid to Liquid: When a solid substance is heated, the kinetic energy of particles increases and they come in random motion and the intermolecular forces of attraction decrease and the interparticle spaces increases , the state of matter changes from solid to liquid and the process is known as melting. eg.
$Ice(s)\, \to \,Water(l)$
Case 2: Liquid to Gas : When a liquid substance is heated, the kinetic energy of particles increases and they came in random motion and the intermolecular forces of attraction decreases and the inter-particle distance increases to a large extent,, the state of matter changes from liquid to gaseous and the process is known as vaporization. .eg.
$Water(l)\, \to \,Steam(g)$
Case 3: Solid to Gas: When a substance (matter) absorbs heat from the surrounding and changes from solid to gas without passing through a liquid state, the process is known as sublimation. eg. Moth balls (Naphthalene balls) will sublime.

Step 2: When matter is cooled or heat is withdrawn:
Case 1: Gas to liquid: When a substance is cooled, it loses thermal energy i.e. kinetic energy decreases, which causes its particles to move slowly and hence the interparticle spaces will decrease and intermolecular forces will increase. The process in which gas changes to liquid is known as condensation. eg.
$Water\,vapours(g)\to Water(l)$
Case 2: Liquid to solid: When more heat is removed from a substance its state is changed from liquid to solid and the process is known as freezing. Eg.
$Water(l)\, \to \,Ice(s)$
Case 3: Gas to solid: This is known as sublimation or deposition. For the deposition to occur, thermal energy must be removed from a gas. Example : in subfreezing ice, water vapour changes directly to ice without first becoming a liquid.

Note: Interconversion from one state to another can be achieved by supplying heat to the substance or by withdrawing the heat from the substance. Heating a substance increases the kinetic energy of particles and they start moving randomly, the interparticle forces of attraction decrease and their state changes. Conversely, cooling particles come closer to each other because of decrease in their kinetic energy.