Physical states of matter
9th chemistry chapter 5 solved exercise short questions
Q#1 : What is diffusion . Explain with an example ?
The spontaneous mixing up of molecules of gases by random motion and collision to form a homogeneous mixture .
The movement of a substance from an area of higher concentration to an area of lower concentration.
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 .
- Pascal (Pa)
- 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 .
- 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 .
” 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 .
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.
” The existence of an element in more than one form in same physical state is called allotropy .”
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 .
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