Change

Q.

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Q. When heated, solid iodine sublimes i.e. it directly changes into a gaseous state without converting to liquid state. Which of the following is NOT true for iodine sublimation?

1. The change is fast.
2. The change is physical.
3. The change is chemical.
4. The change is reversible.

Q.

Sublimation of camphor is a physical change. Explain?

Q.

20. Differentiate between Slow and Fast Changes.

Q.

What is a phase transition, explain with an example?

Q.

When water containing sugar is stirred with a spoon, sugar is dissolved faster. Why does this happen?

1. The spoon acts as a catalyst.

2. On stirring, the temperature increases.

3. Stirring increases the rate of interaction.

4. The attraction between the molecules of sugar increases.

Q. Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel because on heating the iron rim:

1. expands and fits onto the wooden wheel.
2. contracts and fits onto the wooden wheel.
3. no change in the size takes place.
4. expands first, then on cooling contracts and fits onto the wooden wheel.

Q. The burning of paper is a reversible change.

1. True

2. False

Q. When the iron blade is fixed to the wooden handle of tools, it is fitted by _______.

1. cooling followed by heating
2. only heating
3. heating followed by cooling
4. only freezing

Q. Why is burning a candle an irreversible change?

Q. Which of the following is true for physical change?

(i) No new substance is formed.
(ii) The change is reversible
(iii) The change is temporary

1. Only (i)
2. Only (i) and (iii)
3. Only (i) and (ii)
4. (i), (ii) and (iii)

Q.

Explain the change of heat energy in a physical change.

Q.

On heating, metals expand.

1. True
2. False

Q.

The leaves of a tree change their colour in spring before the shed. This is a reversible change.

1. False

2. True

Q. Why melting of butter is reversible whereas curdling of milk is irreversible?

Q.

A change in the physical state can be brought about:

1. only when energy is given to the system

2. only when energy is taken out from the system

3. when energy is either given to or taken out from the system

4. without any energy change

Q.

The 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.

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,

4. Cannot be reversed and can be reversed, respectively

Q.

Why does a camphor tablet get converted to fumes on heating?

Q.

Few iron nails and screws got mixed with wooden shavings while a carpenter was working with them. How can you help him in getting the nails and screws back from the scraps without wasting his time in searching with hands?

Q.

The process of conversion of solids into liquids upon heating is called vaporization.

1. True
2. False

Q.

Which of the following are chemical changes? (i) Decaying of wood (ii) Burning of wood (iii) Sawing of wood (iv) Hammering of a nail into a piece of wood

1. (i) and (ii)

2. (ii) and (iii)

3. (iii) and (iv)

4. (i) and (iv)

Q.

5. In the table given below, one of the changes has been listed under the wrong heading identify this change.

Physical Changes	Chemical Changes
freezing chocolate	the souring of food
whipping cream	making lemonade
squeezing oranges for juice	burning petrol in a motor car

Q. Which of the following property of iron helps it to be separated easily from garbage waste?

1. Lustre
2. Magnetic
3. Sonority
4. Rigidity

Q. When a change can be reversed, meaning when we can get back the original product, it is a reversible change.

1. False
2. True

Q.

An example of a substance that sublimes is ?

1. Florine

2. Bromine

3. Chlorine

4. Iodine

Q. Melting of iron is a change.

1. permanent
2. reversible
3. fast

Q. Forest fire is a reversible change.

1. True
2. False

Q.

Name the following?

A desirable reversible change

Q.

All the changes around us are good.

1. False

2. True