Chemistry
List some Natural changes that occur around us?
Natural changes that occur around us are
- Change of seasons
- Formation of clouds
- Weathering of rocks
- Formation of glaciers
- Flowering in plants
- Ripening of fruits
- Day and night
- Heartbeat and much more.
List some human made changes?
Some human made changes that occur are
- Cooking of food
- Burning of oil
- Cloth weaving
- Dissolving sugar or salt in water
- Food grain production.
Difference between Reversible and Irreversible change?
| Reversible change | Irreversible change |
| The change that can be reversed easily by reversing the conditions to obtain a substance in its original form is called as reversible change. | The change that cannot be reversed even by changing the conditions to obtain a substance in its original form is called as irreversible change. |
| Example Stretching of rubber band, Glowing of electric bulb. | Example Rusting of iron, Burning of Paper etc. |
Difference between Physical and Chemical changes?
| Physical change | Chemical change |
| A change in which no new substances formed is called Physical change. | A change in which a new substance is formed is called as Chemical Change. |
| Chemical composition remains same before and after change. | Chemical composition of the substance changes, so new substances are formed. |
| Most of the physical changes are temporary and can be reversed. | Most of the chemical changes are permanent and cannot be reversed easily. |
| Only physical properties changed. | Both physical and chemical properties change. |
| Example water to ice. | Example Milk to Curd |
Note:
- Melting of wax is a Physical change.
- Burning of Candle is a chemical change.
What are the ways by which changes takes place?
The changes takes place by
- Heating
- Cooling
- Applying pressure
- Mixing
How Heat causes changes?
- Some things become hot on heating and cold on cooling.
- Ex: Water, This process occur in nature.
- Days are warm and nights are cool. Land breeze and sea breeze are also due to heating and cooling of land and sea or ocean water
- Certain things expand, increase in size on heating and contract decrease in size on cooling.
- Ex: Iron and aluminium expand on heating and contract on cooling.
- Wooden handles are fitted into tools such as spades and ploughs.
Certain things change their state
Some things change their state on heating and cooling. Example Ice to water and water vapour.
Equation
Certain combustible substance, such as Candle, Paper Kerosene on heating starts to burning.
What are the changes caused by Pressure?
- Pressure can cause change in shape and size and when released they get back to their original shape.
- Example blowing a balloon or squeezing as Sponge.
What are the changes caused by Mixing?
- When we dissolve salt in water, it gets mixed with water. This is reversible change since we can get back the salt by evaporation technique.
- When quicklime is mixed with water, it is converted to slake lime. It is the chemical and irreversible change.
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