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प्रश्न
What role does energy play in initiating a chemical change ?
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उत्तर
In a chemical change molecules and atoms rearrange themselves to form new substances. This process involves some energy changes. In some changes energy is absorbed
e. g. burning of a substance and in some cases energy is evolved e.g. photosynthesis
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संबंधित प्रश्न
What do you observe when :
a piece of paper is burnt
State whether the following is physical or chemical changes.
passing electric current through a heater rod —
State whether the following is physical or chemical changes.
Melting of wax —
Tick (√) the correct alternative from the choice given for the following statement
Burning is a
Melting of solid (wax) is a physical change.
Give reason.
A dry handkerchief gets wet at once on dipping in water, but it takes longer for a wet handkerchief to dry.
Picture based question
Observe the picture and list down the changes that are accompanied in the picture.
- ______.
- ______.
- ______.
Observe the picture containing a kettle and note that it has salt water in it and answer the following questions:
- What is name of the process that is done to the kettle?
- What will happen to the content of the kettle?
- What kind of change is occurring on the cold surface of the metal plate?
- What can you say about the quality of water that is obtained in the beaker?
Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.
| S. No. | Change | Can be reversed (Yes/No) |
| 1. | The sawing of a piece of wood | |
| 2. | The melting of ice candy | |
| 3. | Dissolving sugar in water | |
| 4. | The cooking of food | |
| 5. | The ripening of a mango | |
| 6. | Souring of milk |
The difference between initial state and the final state is called change.
