Page 2 - 2-Lesson Notes-Common Causes of Physical and Chemical Changes
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2) Chemical reaction:
➢ We know that chemical reactions bring about the chemical changes when two
substances react with each other.
➢ When iron objects are exposed to moist air, a reddish-brown covering of rust
is formed on the surface of the iron. Here, Rust is the new substance formed.
➢ Silver and copper articles and utensils are also seen to be corroded on
exposure to moist air.
➢ Due to this chemical reaction, i.e., corrosion, a black coating appears on silver
articles and a green coating is seen over copper articles.
3) Heating and cooling:
➢ Heating and cooling bring about a change in the physical state of any
substance.
➢ We obtain a boiled egg by heating a raw egg in water.
➢ Burning of a candle, burning of a paper is also due to heat applied.
➢ Freezing of water into ice is an example of the cooling cause of physical
changes.
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