ICSE Chemistry Class 8 Notes Chapter 1 Matter
→ Matter : “Any thing that has mass, occupies volume and can be felt by our senses.”
→ Matter exists in three states
- solid
- liquid
- gaseous.
→ Matter is composed of atoms, molecules or ions.
→ “When molecules are closer, the spaces between them is less, molecular attraction is maximum, i.e., attractive force, molecules have least motion and least K energy hence the substances are solids and have definite shape and definite volume and any number of surfaces.”
→ “When molecules of matter are away from each other, spaces are more, the force of attraction becomes less, molecular motion increases i.e., K.E. increases, hence substance is liquid and have definite volume but no definite shape. Have one upper free surface.
→ “When molecules of matter are far away i.e., spaces are maximum, force of molecular attraction is least, molecular motion increases i.e., K.E. is maximum then the substance is gas. They have no free suface.”
→ Molecular spaces are intermolecular spaces and molecular attraction is intermolecular attraction.
→ Change in matter is brought about on changing temperature or pressure.
→ Melting : “Conversion of solid into liquid by heating.” Iron melts on heating.
→ Vaporisation : “Change of liquid into gas (or vapours) on heating.”
→ Sublimation : “Change of a solid directly into gaseous (vapour) state on heating and on cooling directly back into solid state without changing into liquid state is called sublimation.” Reason is “inter-particle attraction is low.” e.g., Napthalene, iodine, ammonium chloride.
→ Condensation : “Conversion of water vapour to water.
→ Liquefaction : Change of vapour (or gas) into a liquid.
→ Solidification : “Conversion of liquid into a solid” i.e., water to ice.
→ Freezing : “Change of water to ice.”
→ Law of conservation of mass : “Mass can neither be created nor destroyed.”
OR
“In a chemical change total mass of reactants is equal to total mass of product.”
Mass of reactants before reacction = Mass of products after reaction.
