Question

Give reasons for the following –
a.) A gas fills completely the vessels 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 the air but to do the same through a solid block of wood we need a karate expert.

Answer 1

Hint: All these questions can be solved by considering the states of matter and the way molecules are packed in them. For example – molecules in solids are packed very closely and its movement is very restricted, whereas in gas, molecules are free to move.

Complete step by step answer:
The reasons for the given questions are –
A gas fills completely the vessels in which it is kept.
The molecules of a gas are very loosely packed due to intermolecular force of attraction between them. It is because of the lack of any strong binding force that the molecule can randomly move from one place to another. If we fill gas in a vessel, its molecules are free to move and will evenly take up all volume provided to it.

A gas exerts pressure on the walls of the container.
From the above discussion, now we know that molecules of a gas can move around randomly. Therefore, due to this property, gases possess higher kinetic energy. It is because of this random motion and high kinetic energy, that molecules move around and keep hitting other molecules and the surface within which it is stored. Therefore, these factors contribute to gas exerting pressure on the walls of the container.

A wooden table should be called a solid.
Unlike gases, molecules of a solid are bonded by strong intermolecular forces. Therefore, these molecules are packed and do not move around freely. This provides solid strength and rigidity. A wooden table maintains its rigidity and does not flow. Therefore, it is a solid.

We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.
Molecules of a solid are very closely packed, whereas molecules in a gas are very loosely packed. This is majorly because of the force of attraction acting between them. Gases have very little forces of attraction acting between them; therefore, we can easily break it using our hand. Whereas, in solids, intermolecular forces are strong, which cannot be broken easily, therefore we need a karate expert to break a solid block of wood.

Additional Information:
There are two kinds of forces acting between particles – interatomic and intermolecular. Vander Wall forces and Hydrogen bonds are examples of intermolecular forces.

Note: There are three states of matter, namely solids, liquid and gases. We can distinguish it as –
Solid – Rigid, not easily compressible, does not flow.
Liquid – takes the shape of a container in which it is kept, not easily compressible, flows.
Gas – takes the shape of a container in which it is kept, easily compressible, flows easily.