CBSE Notes | Class 6 | Chapter 6 - A Study of Changes | NCERT |

 A Study of Changes

Reversible Change :- A change which can be reversed.

Irreversible Change:- A change in which we can’t get the first object.

Ex. Burning of Paper

Exothermic Change:- A change during which heat is given out (evolved). (gives cold feel)

Ex. Glucose + Saliva

Endothermic Change:- A change during which heat is taken in.

Ex. Melting  Ice Cubes

 

There are many changes which are neither endothermic nor exothermic.

                Salt + Water = Solution

How to classify changes

 

i.                     Physical Change:- A change in which no new substances are formed and which can be reversed by reversing the condition.

Ex.- Change in State of Matter.

Glowing of bulb and heater.

The dissolving of one substance into another.

The expansion and contraction of material.

ii.                   Chemical Change:- A change in which new substances are formed and which can’t be reversed by reversing the condition.

 

A chemical change is also a chemical reaction.

        Reactant + Reactant = Product

Physical Change and Chemical Change both take place together in burning of candle/wax.

Changes can be brought about by one or more of the following methods:-

                Heating or Cooling

                Increasing or decreasing pressure

                Mixing

Science Notes Class 6

1. Matter and it's Nature

2. Food

3. Classification of Material

4. Clothes and Fibre 

5. Separation of Substances

By heating and Cooling:-

i.                     Change in State of Matter.

ii.                   Expansion and Contraction.
Solid < Liquid < Gas

iii.                  Heat can cause irreversible change.
Ex.- burning of paper.

 

By increasing or Decreasing Pressure:-

i.                     Fluffy Solid – Cushion

ii.                   Ductile and Malleable – Solid given desired shape

iii.                  Brittle Solid – Break

Solid < Liquid < Gaseous

Compressed – A gas under pressure.

Mixing things – We can make many physical and chemical change by mixing thing.

                                Physical Changes:- Sugar or salt is  converted into solution

                                Chemical Changes:- Quicklime is converted into slake lime

 

Solid :-

Good Conductor of heat (e.g., metals and alloys)

Expand or Contract on being heated or cooled

Bad conductor of heat (e.g., wood, paper, plastic, etc – becomes hot or cold, but do not obviously expand or contract)

 History Notes Class 6

1. Studying the Past

2. Early Human - I

3. Early Human - II

4. The First Cities

Liquid:-

Expand or contract on being heated or cooled (more than solid do)

 

Gases:-

Expand or Contract much more than solid and liquids do on being heated or cooled

 

 

Aqueous Solution:- A solution in which water is used as the solvent.

Saturated Solution:- A solution that is not capable of dissolving any more solute as a given temperature.

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