Concise Selina Solutions for Class 7 Chemistry Chapter 2 Physical and Chemical Changes

Physical changes are changes affecting the form of a chemical substance, but not it's the chemical composition. Physical changes are used to separate mixtures into their component compounds, but cannot usually be used to separate compounds into chemical elements or simpler compounds. Chemical changes cause a substance to change into an entire substance with a new chemical formula. Chemical changes are also known as chemical reactions. A chemical change is a permanent change. A Physical change affects only physical properties, i.e. shape, size, etc. Examples of chemical changes are burning, cooking, rusting, and rotting. Examples of physical changes are boiling, melting, freezing, and shredding. During a physical change, the arrangement of particles may change, but the mass, the number of atoms and the number of molecules will stay the same. During a chemical change, the mass and number of atoms are conserved, but the number of molecules is not always the same. Chemical reactions involve massive energy changes.