Unit 5 – Physical States of Matter (Short Questions)

Q.1 What is diffusion, explain with an example?
Q.2 Define standard atmospheric pressure. What are its units? How it is related to Pascal?
Q.3 Why are the densities of gases lower than that of liquids?
Q.4 What do you mean by evaporation, how it is affected by surface area?
Q.5 Define the term allotropy with examples.
Q.6 In which form sulphur exists at 100°C?
Q.7 What is the relationship between evaporation and boiling point of a liquid?

Q.1 What is diffusion, explain with an example?
Answer:
The spontaneous mixing of particles of a substance by random motion and collisions, to form a homogeneous mixture is called diffusion.
OR
Movement of molecules of a substance from the region of higher concentration to the region of lower concentration is called diffusion.
Example:
When a few drops of ink are added in beaker of water, ink molecules move around and after a while spread in whole of the beaker. Thus diffusion has taken place.

Q.2 Define standard atmospheric pressure. What are its units? How it is related to Pascal?
Answer:
Standard atmospheric pressure:
It is the pressure exerted by the atmosphere at the sea level. “It is defined as the pressure exerted by a mercury column of 760mm height at sea level”. It is sufficient pressure to support a column of mercury 760mm in height at sea level.
Units:
i. One atmosphere (1 atm): 1 atm is called standard pressure
ii. One pascal (1 Pa)
1atm = 760mmHg = 760torr = 101325Nm^-2 = 101325Pa
(as 1mmHg = 1torr 1Nm^-2 = 1Pa)

Q.3 Why are the densities of gases lower than that of liquids?
Answer:
Gases have lower densities than densities of liquids. It is due to the light mass and more volume occupied by the gases. Another reason for lower densities of gases is negligible intermolecular forces among the gases molecules. On the other hand liquid molecules are closely spaced and have strong intermolecular forces.

Q.4 What do you mean by evaporation, how it is affected by surface area?
Answer:
Evaporation:
“The process of changing of a liquid into a gas phase is called evaporation.” Affect of surface area on evaporation: Evaporation is a surface phenomenon. Greater is surface area, greater is evaporation and vice versa.

Q.5 Define the term allotropy with examples.
Answer:
Allotropy:
“The existence of an element in more than one forms, in same physical state is called allotropy.” Examples:
i. Oxygen has two allotropic forms i.e. oxygen (O2) and ozone (03).
ii. Three allotropic forms of carbon are: Diamond, graphite and bucky balls.

Q.6 In which form sulphur exists at 100°C?
Answer:
Sulphur exists in monoclinic form at 100°C

Q.7 What is the relationship between evaporation and boiling point of a liquid?
Answer:
Relationship between evaporation and boiling point:
If the boiling point of a liquid is high, its evaporations slow. Because intermolecular forces are high in the liquid which have high boiling points. If boiling point is low then evaporation is high.