Changes

Q.

During evaporation the particles of a liquid evaporate from__________

Q.

Changes in which only _________ properties of a substance change are called physical changes.

Q. Explain the mechanism of cleansing action of soaps.

Q.

A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

Q.

107. Generally, the colors of clothes fade away on repeated washing or on exposure to intense sunlight gradually. Explain with a reason.

Q.

(B) Classify the following as physical or chemical change.

13) Baking bread

Q.

Classify the following, as a physical or a chemical change. Give reasons: Change in the colour of black tea on adding lemon juice to it.

Q.

Which is slow process, evaporation or boiling?

Q.

During physical and chemical changes, the energy absorbed or released is

1. Sound energy

2. Heat energy

3. Heat and light energy

4. All of these

Q. Choose the correct answer for the following analogy.
Physical change : Boiling : : Chemical change: _________

1. Melting
2. Condensation
3. Evaporation
4. Burning

Q.

What will happen to the beaker in which the exothermic reaction is carried out?

Q.

Select the correct answer from the choices A, B, C, and D which are given. Write only the letter corresponding to the correct answer.

Two solutions are added together and the new solution becomes hot. This tells you that.

1. A gas is being produced

2. The solutions are not soluble

3. The physical properties are the same

4. A chemical change is taking place.

Q.

(B) Classify the following as physical or chemical change.

(iii) Switching on the bulb

Q.

The products are always on the right-hand side in a chemical reaction.

1. True
2. False

Q.

Give a one-word answer.
Name the term used to represent the substances formed in a chemical reaction.

Q. Which among the following types of change are being depicted in the below figure?

1. Irreversible and chemical
2. Reversible and chemical
3. Irreversible and physical
4. Reversible and physical

Q.

Chemical reactions can be represented using symbols and chemical formulae.

1. True
2. False

Q. Four test tubes are set up at room temperature as shown . Identify the test tube in which a chemical reaction is possible.

1. 
   Magnesium in hydrochloric acid (acid)
2. 
   Copper in water
3. 
   Phosphorus in sodium hydroxide (base)
4. 
   Aluminium in sodium hydroxide (base)

Q.

Digestion is a natural change. Explain.

Q.

As we descend the electrochemical series containing cations, the tendency of the cation to get _________ at the cathode increases.

Q. On heating, the size of a metallic object _________.

1. decreases
2. increases and then decreases
3. increases
4. remains same

Q.

Give scientific reasons for the burning of paper is an irreversible change.

Q. Pure water cannot be obtained back once it is mixed with ________.

1. Petrol
2. Sugar
3. Flour
4. Cooking oil

Q. Pair up the given changes with its respective type.

1. 
2. 
3. 
4. Reversible
5. Chemical
6. Irreversible

Q. On heating, the size of a metallic object _________.

1. increases and then decreases
2. increases
3. remains same
4. decreases

Q. In which of the following changes, the substance can be converted back to its original form?

1. Ripening of fruits
2. Stretching of a rubber band
3. Chopping of vegetables

Q.

6. Rolling of chapati and baking of chapati are the changes that

1. can be reversed

2. cannot be reversed

3. can be reversed and cannot be reversed, respectively

4. cannot be reversed and can be reversed, respectively

Q.

Artificial changes are controlled and performed by__________________________.

Q. The conversion of potato to potato wafers is a _______ change.

1. fast
2. permanent
3. temporary
4. natural

Q. Vapours of ________ phosphorous burn when matchstick is struck against the matchbox.

1. White
2. Red
3. Orange
4. Brown