Say whether True or false
  1. Setting of curd is a chemical change
  2. Burning of wood and cutting it into small pieces are two different types of changes
  3. Blowing of a balloon is fast irreversible change
  4. Chopping of vegetables is reversible physical change
  5. Switching on of the fans is a reversible physical change

1) Settling of curd is a chemical change . True. The original substance is milk and a new substance is formed .ie. curd . Curd is different from the milk and hence is a chemical change.

2) Burning of wood and cutting it into small pieces are both physical and chemical changes. True

Burning of wood and cutting of wood into small pieces are two very different processes. While burning of wood is both a physical and chemical change, the cutting of wood into small pieces only a physical process.  

Wood is basically carbon. So when wood is burnt, the carbon combines with the oxygen present in the air and is converted to carbon dioxide. Also, the unburnt carbon is converted into a black mass. This process also leads to the emission of smoke. Thus we can see that burning of wood is involving the formation of new chemical substances. Also, the overall shape and appearance of wood changes. So it is classified as both a physical and a chemical change. 

On the other hand, cutting of wood into smaller pieces is only a physical process. No chemical  change is taking place as no new chemical substance is being formed. Here only the size of wood is changing. So it is a physical change. 

3) Blowing of balloon is a irreversible change. False . Blowing of balloon is a reversible change . When air is blown into the balloon , its shape and size changes and when air is released from the balloon , it will come back to its original shape . 

4) Chopping of vegetables is irreversible and physical change. The cutting of vegetable is a physical change as shape has been changed and also it cannot be reversed back. 

5) Switching on of the fan is a reversible physical change as it will repeat its motion after a fixed interval of time. 

  • 1
1. True
2. True
3. False
4. False
5. False
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Pl explain question 5 fan...Thanks
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