Physical and Chemical Changes


 

Physical and Chemical Changes logoSubject: Science    Exam: NTSE

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Important Concepts in Physical and Chemical Changes

Find notes, videos, important points and questions to practice on each of these concepts.

  • Physical Changes

  • Chemical Changes

  • Reversible Changes

  • Irreversible Changes



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Important Points

Properties such as shape, size, colour and state of a substance are called its physical properties.
A change in which a substance undergoes a change in its physical properties is called a physical change. A physical change is generally reversible. In such a change no new substance is formed.
A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction.
Examples of physical changes
(a)Change of state (such as from solid to liquid or from gas to liquid)
Specific examples of state change include water freezing, alcohol evaporating and dry ice (solid carbon dioxide) subliming
(b)Absorption of water
(c)Crushing a piece of paper
(d)Pulling copper into a thin wire - a change of shape, but not a change of composition
(e)Cutting a material such as wood
(f)Tearing a piece of tin foil
(g)Breaking glass
(h)Deflating a basketball
(i)Mixing different solids (such as solid sulphur and iron filings)
(j)Inflating a volleyball
(k)Formation of clouds
Examples of chemical changes
(A)Combustion
(a)Burning a log of wood
(b)Explosion of fireworks
(c)Lighting a match
(d)Burning gas in a stove
(e)Roasting a marshmallow
(B)Cooking Examples
(a)popcorn, cake, pancakes, and eggs
(b)Cooking rice
(c)Adding food colouring to icing
(C)Oxidation
(a)Rotting of fruit
(b)Tarnishing silver
(c)Rusting of iron
(d)Oxidizing food for energy
(D)Mixing an acid with a base, producing water and a salt.
(E)Photosynthesis - a process in which carbon dioxide and water are changed into sugars by plants.
(F)Cracking heavy hydrocarbons to create lighter hydrocarbons (part of the process of refining oil).
 
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