Question

Classify the following as chemical or physical changes:
A. Cutting of trees.
B. Melting of butter in a pan
C. Rusting of almirah
D. Boiling of water to form steam
E. Passing of electric current , through water and the water breaking down into hydrogen and oxygen gases.

Answer 1

Hint:: A chemical property is a property of a substance that is observed when a substance undergoes a chemical change. A chemical change is a type of change that also changes the identity of a substance due to breakage and formation of new chemical bonds.
For example: where two substances, A and B, form and break bonds with each other and two other substances, C and D are formed.
Chemical changes and the chemical properties they can produce are directly linked to the physical properties of a substance. Some common physical properties are odor, density, melting point and boiling point, while some common chemical properties are heat of combustion, enthalpy of formation, toxicity, and flammability.

Complete step by step answer:
If the chemical composition is changing then it is a chemical change and if the chemical composition is remaining the same, then it is a physical change.
-cutting of trees –It is a Physical change,as after cutting a tree it regrow
-Melting of butter in a pan – It is a Physical change,as after melting butter we can refrigerate it and it turn back to solid form
-Rusting of almirah –It is a Chemical change,as rusting means when a metal surface get oxidised and there is no turning back to its actual appearance
-Boiling of water to form steam –It is a Physical change.as we can get back water after vapour get condense
-Passing of electric current through water and the water breaking down into hydrogen and oxygen gases -It is a Chemical change.as after breakdown of water molecules it gets converted into ions which later turns into gases.

Note:
-The most important thing for you to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change
Whereas in chemical reaction, Change in Color. A change in color is also another characteristic of a chemical reaction taking place
When two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place and also formation of a Precipitate,Formation of Bubbles.