Physical states of matter

9th chemistry chapter 5 solved exercise short questions

Q#1 : What is diffusion . Explain with an example ?

Diffusion:

The spontaneous mixing up of molecules of gases by random motion and collision to form a homogeneous mixture .

or

The movement of a substance from an area of higher concentration to an area of lower concentration.

Example :

When a few drops of ink are added in a beaker of water , ink molecule diffuse around to form homogeneous mixture .

Q#2 : Define standard atmospheric pressure . What are its units ? How it is related to Pascal ?

Standard Atmospheric Pressure :

It is defined as :

“The pressure exerted by a mercury column of 760 mm height at sea level “

• It is sufficient pressure to support a column of mercury 760mm in height at sea level .

Units :

1. Pascal (Pa)
2. atm
3. torr (mm of Hg)

Relation with pascal :

1 atm = 760 mm of Hg = 760 torr

( 1 mm of Hg = 1 torr )

= 101325 Nm-2 =101325 Pa

Q#3 : Why are the densities of gases lower than that of liquids ?

Densities of gases :

Gases have lower densities then liquids and solids .

Reason :

• It is due to the lower mass and more volume occupied by the gases .
• That’s why mass of unit volume of gases is less as compared to liquids and solids .

Q#4 : What do you mean by evaporation how it is affected by the surface area .

Evaporation :

” The process of changing of a liquid into gaseous phase at all temperature is called evaporation .”

Effect of Surface Area:

Evaporation is a surface phenomenon .Greater is surface area , greater is evaporation and vice versa .

Example :

Sometimes , a saucer is used if tea is to be cooled quickly .This is because evaporation from the larger surface area of saucer is more than from the smaller surface area of a tea cup .

Q#5 : Define the term allotropy with examples.

Allotropy :

” The existence of an element in more than one form in same physical state is called allotropy .”

Example :

Oxygen have two allotropic forms

i.e., diatomic oxygen ( O2 ) and ozone ( O₃ ).

Q#6 : In which form sulphur exists at 100 °C .

Sulphur exists in monoclinic form at 100 °C.

Q#7 : What is the relationship between evaporation and boiling point of a liquid ?

Relationship between Evaporation and Boiling Point :

If the boiling point of a liquid is high , its evaporation is slow .

• Because intermolecular forces are greater in liquids which have high boiling points .
• If boiling point is low then evaporation is high .

9th Chemistry Chapter 5 solved exercise MCQs

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