Changes Around Us - UPSC Sci & Tech Free MCQ Test with solutions

I) The changes where the physical property of the substance varies without any formation of new products.
ii) These changes are reversible and the products are identical to the reactants.
Ex: Melting of ice, during this change the water changes from its solid form to liquid form, melting of wax.

In physical changes no new substance is formed and can be returned back by physical process.

When a material is heated, the kinetic energy of that material increases and its atoms and molecules move about more. This means that each atom will take up more space due to its movement so the material will expand.

Melting of ice into water is a physical change as no new substance is formed with different properties.

An atom is the smallest particle of an element which cannot be seen with naked eyes.

Formation of a compound is chemical change as it is a permanent change

Those changes in which change can be reversed back is called as reversible change as melting of ice.

Chemical changes are changes that occur in the chemical properties of the substance like its flammability, radioactivity, etc. All chemical changes are mostly irreversible changes. Once the chemical properties of a substance are changed, it becomes another substance. Thus, it cannot return to its original state in most cases.

In chemical change, molecules of a substance and rearrange in different order to produce new character.

Sea water is a mixture as it contains a number of salts dissolved in it but not in fixed ratio.

A reversible change is a physical change that can be undone. A final substance can be converted back to the original substance without creating any new material. Freezing, melting, dissolving, boiling, evaporating and condensing are reversible changes.

A chemical change (chemical reaction) is a change of materials into other, new materials with different properties, and one or new substances are formed. Burning of wood is a chemical change as new substances which cannot be changed back (e.g. carbon dioxide) are formed.

In a chemical change molecules of substance change and rearranged to change into new product.

A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs. Physical changes are usually reversible.

Burning of candle is both physical and chemical change as wax first melt which is a physical change and burning of wick is a chemical change that produce carbon dioxide gas.

Change in season is periodic change as it is repeated at regular interval of time.

Rusting of iron is a chemical change as new substance rust is formed with different property.

Souring of milk is undesirable change as milk gets spoiled due to souring which is not desired.

The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.

Boiling of water is an example of physical change as water vapour can be changes into water by cooling.