Defination of phase

Defination : A phase is physically distinct and mechanically separable homogenous part of surface.A system consisting of One phase is called Homogenous system and a system consisting of two or more phase is called heterogeneous system. Example: 1) The decomposition of CaCO3 When CaCO3 is Heated in a closed vessel CaCO3 ———> CaO + CO2 (Solid) (Solid) (gas) There is two solid phase and one gaseous phase . Hence it is 3- phase system. 2 ) H2O is Present in three phases : SOLID (ICE) , LIQUID (WATER) AND GAS(WATER VAPOUR) 3 ) NaCl (Common salt) mixed with Water ,it is a single Phase system because NaCl completely mixed with water and there is no mechanically separable line is present