[5 Mark Question Answer]

Question 15 Marks

Discuss the three states of matter solid, liquids and gas on the basis of molecular model.

Answer

Solids

Here the molecules are very tightly packed that there is no or very less intermolecular space and there is a high intermolecular force of attraction $($force of cohesion$)$. The molecules do not move about their mean position and thus solids have a definite shape and volume.
Liquids

Here the molecules are less tightly packed as compared to solids and also there is a lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they do not have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.
Gases :

Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which results in the weakest intermolecular forces of attraction. The molecules as are not bound by any strong force, move about freely and thus gases do not have a definite shape and also do not have any definite volume.

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Question 25 Marks

What do you mean by the inter$-$molecular spaces? How do they vary in different states of matter?

Answer

INTER-MOLECULAR SPACES “The spacing between the molecules of the matter is called Inter$-$molecular spaces.”
The inter$-$molecular spaces in different states of matter:
The intermolecular space between solids is absent.
The intermolecular space between Liquid is moderate but present.
The intermolecular space between gasses is free$-$flowing and plenty.
Explanation of inter$-$molecular space : Take water in a measuring cylinder say up to $80\ ml$. mark. Add $10\ gm$ of salt to it. The volume in the cylinder should increase. On dissolving salt we find volume remains same i.e. up to $80\ ml$ mark. This is because there are spaces in water molecules and salt molecules occupy these spaces and volume remains the same.

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Question 35 Marks

Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.

Answer

BOILING POINT OF WATER AT CONSTANT TEMPERATURE:
Take some water in a beaker. Suspend and clamp a thermometer in a beaker in water so that the bulb of thermometer remains in water without touching bottom and sides of the beaker. Supply heat by the burner and note the temperature at room temperature $(20^\circ C$ nearly$)$

Record the temperature after every minute. The temperature rises and as it reaches $100^\circ C$ water starts boiling. Though heat is being supplied temperature does not rise i.e. it remains constant at $100^\circ C$ and bubbles formed are seen. Thus, the boiling point of water is $100^\circ C$ and at boiling point heat supplied is absorbed by water at a constant temperature. Because this heat is being used to change every molecule of water into vapours.

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Question 45 Marks

Match the following

Column $A$		Column $B$
$(a)$	Molecules	$(i)$	Water boils
$(b)$	$100^\circ C$	$(ii)$	Evaporation
$(c)$	$0^\circ C$	$(iii)$	Changes from solid to gas
$(d)$	At all temperatures	$(iv)$	Matter
$(e)$	Camphor	$(v)$	Water freezes

Answer

Column $A$		Column $B$
$(a)$	Molecules	$(iv)$	Matter
$(b)$	$100^\circ C$	$(i)$	Water boils
$(c)$	$0^\circ C$	$(v)$	Water freezes
$(d)$	At all temperatures	$(ii)$	Evaporation
$(e)$	Camphor	$(iii)$	Changes from solid to gas

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