States of matter chemistry class 11 includes the concept of intermolecular forces. Every relation needs a force. The force which combines molecules together is called intermolecular force. Students could be confusing it with the bonding force of molecules. The force which exists between two molecules is intermolecular force and the force which is within the molecule is called intramolecular force. The bonding between family members is intra-bonding, and the bonding of family with neighbors is inter-bonding. You must also have heard about intra-school competitions, which are competitions within the school. Intermolecular forces are both attractive and repulsive. Attractive intermolecular forces are also known as Van der Waals forces.

Van der Waals forces are three types:

1. London force
2. Dipole-dipole force
3. Dipole-induced dipole forces

NCERT Solutions Class 11 chemistry explains the concept of thermal energy. Thermal energy is heat. When you heat molecules, the molecules start moving, and this energy is called thermal energy. Thermal energy is directly proportional to heat. If you raise the heat, the thermal energy also increases. The motion of molecules because of heat is called thermal motion. Here, the thermal energy concept is important to know how matter changes its state.

Intermolecular Forces vs. Thermal Interactions

When we increase intermolecular force, matter changes from gas to liquid to gas. When we increase thermal energy, matter changes from solid to liquid to gas. Gas has the highest thermal energy, and this is why it moves around. State of matter chapter 11 has other concepts as well, which will be discussed further.

Chapter 5, chemistry, class 11, includes the gaseous state of matter. If we see the periodic table, out of 118 elements, only 11 elements are gas. But still, they have great importance, which is why we will discuss them in detail.

Gas Properties:

• The force between two gas molecules is negligible.
• Gas moves from one place to another freely.
• Gases can be compressed highly.
• Shapes and volume are not fixed.
• Gas exert pressure in all directions equally.
• The density of gases is lower than the solids and liquids.
• Gases mix together easily without any extra effort.

Gas Laws are included in NCERT Solutions Chemistry Class 11.  The laws are driven by experimental studies. The laws are the relationship between measurable properties of gases: Mass, volume, pressure, and temperature. There are three types of laws: Boyle’s Law, Charles Law, and Avogadro Law.

Boyle’s Law: In 1662, Boyle’s law was discovered by Robert A. Boyle. Boyle’s law says that if we fix the temperature, then the pressure exerted by the gas is inversely proportional to the volume of gas. The formula of Boyle’s Law is pV=k where, p= pressure of the gas, V=Volume of the gas, k=constant.

Charles Law: The concept of Charles law is that the temperature of gas and volume of gas is directly proportional to each other. The example of Charles Law is when an overfilled tire bursts in the hot sun and in cold temperature, it is advised to check the air of the tire.

Avogadro Law: The Avogadro law states that the volume of gas and the total number of atoms are directly proportional. The example of the law is when we breathe and take air inside the lungs, lungs expand. Another example is a balloon. When air is filled, the balloon expands. The formula of Avogadro Law is   PV=nRT, where P=pressure exerted by the gas, V=Volume of gas, n=Number of molecules, R=Universal Gas Constant, T=Temperature of gas.

Ideal Gas Equation

A gas that follows Boyle’s Law, Charles Law, and Avogadro Law is called an Ideal Gas. It is a hypothetical concept. In reality, no gas is ideal.

Ideal gas equation

pV=nRT  where R=Universal Gas constant, p= pressure, V= Volume, T=Temperature, n= number of molecules.

In molecular speed, we never talk about a single molecule. Every molecule has a different speed. We talk about three types of speed: average speed, most probable speed, root means square speed.

Kinetic Molecular Theory of Gases

Why does gas behave in such a way? When we increase temperature, pressure will increase. If we make temperature constant and increase pressure, the volume will decrease. It is explained in the Kinetic molecular theory of gases. Molecular speed depends on two factors:

• Temperature
• Mass

We see that if we make temperature constant, fewer mass molecules’ speeds will be high.

The Behavior of Real Gases: Deviation from Ideal Gas Behaviour

Now, we will discuss the reasons why real gases deviate from ideal gas behavior. A real gas is a gas that is seen in the real world and deviates from an ideal gas. The reason for the deviation is the assumptions of an ideal gas. The assumption of ideal gas states that if pressure increases, then volume decreases. But it is not the case for all real gases. In hydrogen and helium gas, volume increases when the pressure increases. With Methane and carbon dioxide, initially, in these gas volumes decreases, but then after one point starts increasing. The volume of gas could be very less but not zero.

Liquefaction of Gases

The process in which gas converts into liquid is called liquefaction of gas. It happens when the pressure on gas increases and the temperature of gas reduces. The gas molecules get closure together and convert into gas.

Liquid State

The intermolecular forces are stronger in the liquid state compared to the gaseous state. In liquid, molecules are quite close, and there is very little space between them.

Here are the NCERT solutions to Chapter 5 Chemistry Class 11.

Example 2

Example 3

Example 4

Example 5

1. What are the 5 basic states of matter?

There are five states of matter which are solid, liquid, gas, plasma, Bose-Einstein condensate. The Bose-Einstein condensate state is human-made.

2. What is the meaning of thermal energy?

Thermal energy is energy that is responsible for the temperature of matter. The rise of temperature leads to the generation of thermal energy.

3. What is the meaning of Matter? 

According to Chapter 5 Chemistry Class 11, any substance which needs space and mass is matter.