Cooling from Evaporation

Q. Identify the reversible change/changes among the following:
Change 1 - Boiling of water
Change 2 - Burning of wood
Change 3 - Stretching of a rubber band

1. Only 3 is a reversible change.
2. Only 1 is a reversible change.
3. Both 1 and 2 are reversible changes.
4. Both 1 and 3 are reversible changes.

Q. Salt can be recovered from its solution by evaporation. Choose some other technique for the same.

1. Filtration
2. Sedimentation
3. Crystallisation
4. Chromatography

Q. While lighting a candle, Paheli observed the following changes:
(i) Wax was melting.
(ii) Candle was burning.
(iii) Size of the candle was reduced.
(iv) Melted wax was getting solidified.
Of the above, the changes that can be reversed are

1. (i) and (ii)
2. (ii) and (iii)
3. (iii) and (iv)
4. (i) and (iv)

Q. Give reason:
a. Sugar and water can be separated by crystallisation technique.
b. Salt from seawater can be separated by evaporation technique.

Q. Conversion of ice into water and water into ice is an example of change that can be reversed. Give four more examples where you can say that the changes can be reversed.

Q. Changes that lead to the formation of new substances are called

Q. The change of a bud into a flower is a change that cannot be reversed. Give four more such examples.

Q. Which of the following changes are irreversible in nature?

1. Melting of candle wax
2. Dissolution of sugar in water
3. Setting of cement
4. Woolen yarn to knitted sweater

Q.

1. How do you define a chemical change?

2. Give two or three examples of chemical change.

3. Choose the correct characteristic(s) about the chemical change from the following

Characteristic 1: chemical changes are irreversible

Characteristic 2: new substances are formed.

Characteristic 3: properties of new substances are the same as the properties of original substances.

Q. Clothes made of _________ fibres are preferred in summer.

1. jute
2. cotton
3. silk
4. woollen

Q. Which type of clothes are preferred during the summer season?

1. Woollen
2. Cotton
3. Jute
4. Silk

Q. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain this observation.

Q.

Why should we wear cotton clothes in summer?

1. Cotton provides better air circulation.

2. Cotton is a good absorber.

3. Cotton provides better air circulation and a good absorber.

4. There are more patterns availible.

Q.

what is the difference in sublimation process and heating

Q. Match the given objects below with the materials from which they could be made. Remember, an object could be made from more than one material, and a given material could be used for making many objects.​

Objects​	Materials​
Book​	Glass​
Tumbler ​	Wood​
Chair ​	Paper ​
Toy​	Leather ​
Shoes​	Plastic​

Q. In which of the following processes do the change in the states of matter involve the absorption of energy?
A. Boiling
B. Sublimation
C. Condensation
D. Melting

1. A only
2. A, B and C only
3. A and B only
4. A, B and D

Q. Changes that lead to the formation of new substances are called

Q. The following image shows the image of a lid which is used to close a vessel containing hot cooked rice. Identify the property which is undergoing a change and its cause.

1. Change in colour, solidification
2. Change in smell, condensation
3. Change in state, condensation
4. Change in taste, solidification

Q. Clothes made of _________ fibres are preferred in summer.

1. cotton
2. silk
3. woollen
4. jute