A substance is any material with distinct physical and chemical properties that occupies space and has mass. It can exist in solid liquid or gaseous states and may be pure like elements and compounds or a mixture. Substances play a key role in physical and chemical processes around us.
Chapter 10 Thermal Properties of Matter in Class 11 Physics explains the behavior of materials under temperature changes. It covers concepts like heat transfer specific heat thermal expansion and temperature scales. Understanding conduction convection and radiation along with the laws governing them helps in practical applications like thermometry and material science.
A change of state is the transformation of a substance from one physical phase or state of matter to another. The three most common states of matter are solid, liquid, and gas. A substance can change between these states due to the addition or removal of heat energy. The change of state involves changes in the arrangement and energy of the particles (atoms or molecules) that make up the substance.
Types of Changes of State:
1. Melting (Solid to Liquid):
– When the solid is heated, the energy of the particles increases, causing them to move more freely until they break away from each other. The end result is the solid turns to liquid.
Example: Ice turns to water due to melting.
2. Freezing (Liquid to Solid):
– When a liquid is cooled, the particles lose energy and move slowly; thus, they can form bonds and arrange themselves in an orderly structure to make the liquid become a solid.
Example: Water freezes to ice.
3. Vaporization (Liquid to Gas):
This happens when a liquid is heated; the particles receive enough energy so that they would be able to overcome the forces holding them in place, break free, and escape into the gas phase by vaporization. Included in this are evaporation through the surface of a liquid at any temperature, and boiling that occurs throughout a liquid at specific temperatures. Example: boiling water into steam.
4. Condensation from Gas to Liquid
– When a gas is cooled, the particles lose energy, slow down, and come closer together, forming liquid droplets.
Example: Water vapor condensing on a cold surface.
5. Sublimation (Solid to Gas):
– Change of phase from solid directly to gas, bypassing the liquid phase. This takes place when the solid particles acquire sufficient energy to break free from their bonds, dispersing themselves as gas particles.
– Dry ice is the solid carbon dioxide sublimating to carbon dioxide gas.
6. Deposition (Gas to Solid):
– Deposition is the opposite of sublimation, where a gas transforms directly into a solid without going through the liquid phase. This happens when gas particles lose enough energy to settle into a solid structure.
Example: Frost forming from water vapor in the air.
Factors Affecting the Change of State:
– Temperature: The addition of heat energy raises the temperature, and the substance can change from solid to liquid or from liquid to gas, such as melting or vaporization. Cooling the substance will cause the opposite changes, like freezing or condensation.
Pressure applied to a substance can also be a variable. For example, increasing the pressure can make a gas condense into a liquid or even a liquid freeze into a solid.
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