Class 5th - Science L3

MATTER

IV. Answer the following questions.

1. How does a an element differ from a compound?

Ans. An element is made up of only one kind of atom. A compound is made up of more than one kind of atom. 

2. What determines the state of matter?

Ans. The arrangement of molecules and the force of attraction between them determine the state of matter. 

3. Why do liquid flow?

Ans. The force of attraction between the molecules of a liquid is weak. However, it is enough to not allow the molecules to move far apart from each other. The molecules in a liquid are, therefore, arranged slightly away from each other. This allows some movement between the molecules. That is why liquid flows. 

4. A solid substance changes to a liquid on heating. Why?

Ans. Heating changes the arrangement of molecules in a substance and, thereby, changes its state. On heating, the molecules gain energy and move further apart. Hence, when a solid is heated, it changes into a liquid. 

5. What kind of change is a temporary change?  Explain such a change with an example.

Ans. A physical change is a temporary change. It does not result in the formation of a new substance as the properties of the substance do not change. For example, the formation of a salt solution is a physical change because both salt and water can be easily separated. Also, a physical change is mostly reversible. When water vapour cools, it changes back into water.  

V. Do as directed

1. Draw a diagram to describe the molecule of oxygen and justify why oxygen is an element. Name another element.

 

 O=O

Ans. Oxygen is made of only one kind of atom. Hence, it is an element.

Chorine is also an element.

 

2. Draw a diagram of the ammonia molecule and justify why ammonia is a compound. Give another example of a compound.

H=N=H      H

 

Ans  Ammonia is made of up of two different molecules - nitrogen and hydrogen. Hence, it is a compound. Water is also a compound.

3. Explain why the molecule of carbon dioxide gas spread throughout the entire available space.

Ans. There is hardly any force of attraction between the molecules of carbon dioxidgas. This allows the molecules to move freely and spread throughout the entire available space.

4. Give an example of a chemical change. Explain why it is a chemical change.

Ans. A chemical change forms one or more new substances. A chemical change is mostly irreversible and permanent. For example, the burning of paper brings about a chemical change. The paper is reduced to ash. The new substance formed is ash. Ash cannot be converted into paper again. 

5. What kind of change is mostly a temporary change? Explain such a change with ab example.

Ans. A physical change is a temporary change. It does not result in the formation of a new substance as the properties of the substance do not change. For example, the formation of a salt solution is a physical change because both salt and water can be easily separated. Also, a physical change is mostly reversible. When water vapour cools, it changes back into water.

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