Ideal Gas Law: Overview, Questions, Preparation

As a result of experimental studies, the gas laws are relationships between the measurable properties of gases like Pressure, Temperature, Volume, and Mass. The relationship between these variables can describe the state of a gas.

The research on the physical properties of gases leads to the discovery of Gas Laws. There are three gas laws; Boyle's Law, Charles's law, and Avogadro's Law. A gas that follows all three laws is ideal.

At a constant temperature, the pressure of a fixed amount of gas (number of moles, n) varies inversely with its volume. At constant t and n, 

                     p ∝ 1/V

                     p = K₁ 1/V

K is a proportionality constant. At a constant temperature, the product of volume and pressure of a fixed amount of gas is constant.

                    K = pV

Reference: NCERT

The graph shows that as the pressure decreases, volume increases.

At a constant pressure, the volume of a fixed mass of gas will be directly proportional to its absolute temperature.

                   V ∝ T

                 V = KT

                 K =V/T

The constant value is determined by the pressure of a gas, its amount, and the volume.

Reference: NCERT

The chart shows that as the Volume increases, Temperature increases.

The Law states that equal volumes of gases contain an equal number of molecules under identical temperature and pressure conditions.

                 V ∝ n, n is the number of moles.

                V =K n

For one mole of a gas, the number of molecules present is 6.022× 10²³. It is known as the Avogadro constant.

The three laws combine in a single equation is known as the Ideal gas equation.

At constant T and n; p ∝ 1/V

At constant p and n; V ∝ T 

At constant p and T; V ∝ n 

Thus,

Reference: NCERT

The above equation represents an Ideal gas equation. R’s value is the same for all gases, and the numerical value of R depends upon units in which p, V and T are measured. So, R is a Universal Gas constant.

R = 8.3145 Joules · mol-1 · K-1 (SI Unit) = 0.082057 L · atm·K-1 · mol-1

The chapter explains the laws governing the behaviour of ideal and real gases. It also deals with how to apply gas laws in different situations. This topic's weightage is 5 marks, and the questions on gas laws expressions and graphs, Ideal gas Equation, and numerical on gas laws.

     P₁V₁ =P₂V₂

1 x 500 = P₂ x 200 ; P₂=500/200 =2.5 bar

2. At room temperature, the 120 mL capacity vessel has 1.2 bar pressure. The gas is transferred to another vessel of volume 180 mL. What would be its pressure?

V₁= 120 mL, P₁=1.2 bar, V₂ = 180 mL

  P₁V₁ =P₂V₂

(1.2 ) (120) = P₂ (180) P₂ =0.8 bar

3. Using the Ideal gas equation pV=nRT, show that a given temperature density of a gas is proportional to gas pressure p.

Ideal gas Equation pV =nRT

Q: Why Ideal gas equation is known as the Equation of state?

Q: State Gay Laussac’s law?

Q: What is the Equation that represents Combined Gas law?

A:

Q: What is isochore and isobar?

Q: How to evaluate the value of the gas constant?