Changes Around Us Test - 2

The sign indicates a reversible process in which the product molecules recombine to form reactant molecules and the reaction is reversible.

Milk converted to curd, mango converted to mango pickle, and animal waste converted to manure are examples of the changes which cannot be reversed.

Inter-conversion of states of water, e.g., steam to ice, can easily be reversed by changing the temperature and pressure conditions.

Sublimation is a process by which a solid on heating converts to vapour without going into the liquid state.

This is a physical change.

A chemical reaction involves the formation of a new substance having properties different from those of the reacting species.

The new substances formed are referred to as products.

Oxidation of a substance is a chemical change.

During oxidation, the substance reacts with oxygen or another electronegative element to form a new substance, having properties different from those of the reacting substance.

Combination reactions are always exothermic.

Concrete is initially fluid, but with time it crystallises and sets into a hard mass of dense material. This is an irreversible process because once set, the concrete cannot be made fluid again.

Mixing of salt in water is a reversible change because the components of the mixture can be separated by evaporation. Water vaporises and salt is left behind.

Thus, dissolution of salt in water is a reversible change.