## Topic outline

• ### Matter in Our Surroundings

#### Q100. (a) Tabulate the differences in the characteristics of states of matter.(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Ans. (a) Differences in the characteristics of 3 states of matter are:

 Characteristics Solid Liquid Gas Shape Fixed shape No fixed shape No fixed shape Volume Fixed volume Fixed volume No fixed volume Intermolecular force Maximum Less than solids Very less Intermolecular space Very less More than solids Maximum Rigidity/Fluidity Rigid/Cannot flow Not rigid/Can flow Not rigid/Can flow Compressibility Negligible Compressible Highly compressible

(b) Rigidity - The tendency of a substance to retain/maintain their shape when subjected to outside force.

Compressibility - Compressibility is a measure of the relative volume change of a fluid or solid as a response to a pressure change.

Fluidity - The tendency of particles to flow is called fluidity.

Filling a gas container – When a gas is put in an empty container, it quickly spreads throughout the container and fills it completely.

Shape – It means a definite boundary. Only solid has definite shape.

Kinetic energy - The kinetic energy of an object is the energy that it possesses due to its motion.

Density - The density of a substance is its mass per unit volume.

#### Q101. Give reasons(a) A gas fills completely the vessel in which it is kept.(b) A gas exerts pressure on the walls of the container.(c) A wooden table should be called a solid.(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

Ans. (a) A gas fills completely the vessel in which it is kept because due to high kinetic energy and negligible forces of attraction, the particles of a gas are moving with high speeds in all directions.

(b) Because of high kinetic energy and negligible forces of attraction, the particles of a gas move with high speeds in all directions. When the fast moving gas particles hit the walls of the container, they exert a pressure (called gas pressure). Thus, a gas exerts pressure on the walls of the container.

(c) A wooden table should be called a solid because it possesses all the properties of a solid such as

1. It has a fixed shape.

2. It cannot be compressed much.

3. It has a high density.

(d) We can move our hand through air easily because the force of attraction between the particles of air is very weak. But we cannot move our hand through a solid block of wood because the force of attraction between the particles of wood is very strong.