# Chapter 7 – Study of Gas laws

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

We all feel gas but are unable to see it. Have you ever wondered what you mean by gas or how you define it? What are the major examples of gas? Nitrogen, oxygen, hydrogen, fluorine, and chlorine are some of the major gases we see every day.

We know that oxygen is one of the major gases which we use for breathing every day.

#### What are Gas Laws?

Gas laws are the major group of laws that govern the behaviour of gases:

• The volume occupied by the gas
• The pressure exerted by the gas on the container walls
• The temperature of the gas
• Amount of the gaseous substance

#### Studying Gas Laws

The study of gas laws came into existence way back in the 17th century. Since then, scientists have been using these gas laws to find out the pressure, volume, temperature, and many other details about the gas.

The five major gas laws are –

• Boyle’s Law
• Charles’s Law
• Gay-Lussac’s Law
• The Combined Gas Law

#### Boyle's Law

This relationship involves the relationship between pressure and temperature of the gas at a specific temperature. The pressure of the gas is inversely proportional to the volume of the gas.

Boyle’s Law equation is written as –

V ∝ 1/P

P ∝ 1/V

PV = k1

Where, V – Volume of the gas

P – Pressure of the gas

K1 – Constant

#### Charles's Law

As per this law, in a closed system and at a constant temperature volume of the gas, it is directly proportional to the gas’s temperature.

Charle’s law equation is written as –

V ∝ T

Where, V – Volume of the gas

T – Temperature of the gas

#### Gay-Lussac's Law

The law states that, at a certain volume, the gas’s pressure is directly proportional to the temperature of the gas. When heat is applied to the gas, the molecules move faster and gain more energy, whereas when the molecules cool down, then the same happens.

Gay Lussac Law is written as –

P ∝ T

Where, P – Pressure of the gas

T – Temperature of the gas

This law states that the gas is ideal, and thus the same number of molecules exist in the same system.

Avogadro’s law is written as –

V / n = constant

Where, V – Volume of the gas

n – Number of molecules in the gas

#### Combined Gas Law

This is also known as the gas equation, a combination of three major gas laws – Charle’s Law, Boyle’s Law, and Hay Lussac Law. In this law, the relationship is shown between temperature, volume, and pressure of the gas.

Combined Gas Law is written as –

PV / T = k

Where, P – Pressure of the Gas

V – Volume of the gas

T – Temperature of the gas

k – Kinetic Energy

#### Relationship Between Kelvin Scale and Celsius Scale of Temperature

The temperature measurement scales are expressed with three units – Celsius, Kelvin, and Fahrenheit. But there is a slight difference between the Celsius and Kelvin scale. And this difference lies in the zero points. Kelvin’s zero points are 273.15 more than the Celsius degrees.

#### Conclusion

This chapter covers gases and their properties, along with the different laws that determine the gas’s behaviour and properties. The different scales of measurement and the relationship between them are also covered under this topic.

#### FAQs

1. What is the significance of the Kelvin scale of temperature?
It was challenging to express the behaviour of gases below 273.15 C. Thus, the kelvin scale of temperature was devised.
2. What is the significance of Charles’s Law?
The volume of the given mass is directly proportional to the temperature, and the density also decreases along with the temperature. One example of Charles’s law application is hot air, filled in balloons and used for meteorological purposes.
3. What is the boiling point of water on the Kelvin scale? Convert the same into the centigrade scale.
On the Kelvin scale, the boiling point of water is 373 K. Since 273 K is the conversion point, the boiling point of water on the centigrade scale is 373 – 273 = 100 degrees Celsius.
4. What is the kinetic theory of matter?
The kinetic theory of matter states that the number of molecules present in a given state of mass and the average particles inside it is always constant.
5. What is the relevance of Boyle’s law?
As the pressure increases, the volume decreases, and the gas becomes much denser. Thus, the pressure is directly proportional to the gas’s density at any given point of temperature. Atmospheric temperature is less at the high altitude areas, and the gas is also less dense. It is why mountaineers carry an oxygen cylinder with themselves, as the oxygen level is quite less at the top.
6. What are the three variables of the gas laws?
The three variables of the gas laws are volume, pressure, and temperature.

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