Gas Laws

Gas Laws, When the conditions are normal, all gases have similar behaviour. However, even slight changes in physical conditions such as pressure, temperature, or volume cause a deviation. The behaviour of gases is studied using gas laws. A gas’s state variables, such as pressure, volume, and temperature, reveal its real nature. As a result, gas laws are the relationships that exist between these variables. Let’s learn more about the crucial gas rules!

What Are the Gas Laws?

The gas laws are a set of rules that control the behaviour of gases by establishing correlations between the following variables:

• The amount of space occupied by gas.
• The force that a gas exerts on the container’s walls.
• The gas’s absolute temperature.
• The quantity of a gaseous material (or the number of moles of gas).

All gases behave similarly under ordinary conditions. When the physical parameters related to the gas (such as temperature, pressure, and volume) are changed, alterations in their behaviour occur. The gas laws, which were named after the scientists who discovered them, essentially describe the behaviour of gases.

Gas Laws

In the late 18th century, a series of gas laws were formulated by various scientists, and the laws are named after them. Here are the principal gas laws:

• Boyle’s Law: Describes the inverse relationship between the pressure and volume of a gas at constant temperature.
• Charles’s Law: States that the volume of a gas is directly proportional to its absolute temperature, assuming pressure remains constant.
• Gay-Lussac’s Law: Explains that the pressure of a gas is directly proportional to its absolute temperature when volume is kept constant.
• Avogadro’s Law: Indicates that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of the gas.
• Combined Gas Law: Integrates the previous three laws to relate pressure, volume, and temperature. The Ideal Gas Law further incorporates the molar amount of the gas into this relationship.

Under typical conditions, gases behave similarly; however, their behaviors can differ when conditions such as temperature, pressure, and volume change. These gas laws provide a foundational understanding of how gases behave under different conditions and are key in both academic study and practical applications. The laws are summarized and explored in depth, along with additional underlying principles.

When the conditions are normal, all gases exhibit comparable behaviour. However, a little change in physical variables like as pressure, temperature, or volume causes a divergence. Gas laws are an examination of the behaviour of gases. A gas’s state variables, such as pressure, volume, and temperature, reveal its true nature. As a result, gas laws are relationships between these variables.

Boyle’s Law

At constant temperature, Boyle’s law describes the relationship between a gas’s pressure and volume. So, according to Boyle’s law, doubling the pressure reduces the volume of a gas by half at a constant temperature. The explanation for this is the intermolecular force that exists between the molecules of a gaseous substance. Because of the distributed molecules, a gaseous substance fills a larger volume of the container in its free condition. When pressure is applied to a gaseous medium, the molecules move closer together and take up less space. In other words, the applied pressure is proportional to the density of the gas. The volume of a gas is inversely proportional to its pressure under constant temperature. Its formula is as follows:

PV=k₁

Boyle’s Law can be used to calculate the current pressure or volume of a gas and is also written as

P₁V₁=P₂V₂

Charle’s Law

In 1787, Jacques Charles studied the impact of temperature on the volume of a gaseous substance under constant pressure. He conducted this research to better understand the technology behind hot air balloon flights. According to Charle’s law, the volume of a gas in a closed system with constant pressure is directly proportional to the temperature (in Kelvin). This means that as the temperature rises, the volume rises, and as the temperature falls, the volume falls. This law essentially outlines the relationship between the temperature and volume of a gas. Charle’s law can be stated mathematically as;

V₁ / T₁ = V₂ / T₂

Gay-Lussac Law

The Gay-Lussac equation expresses the relationship between temperature and pressure at constant volume. The law asserts that for a particular gas, the pressure is directly proportional to the temperature at a constant volume. When you heat up a gas, the molecules gain energy and travel quicker. When the molecules are cooled, they slow down and the pressure lowers. The Gay-Lussac law, which is mathematically written as; can be used to determine the change in temperature and pressure.

P₁ / T₁ = P₂ / T₂

Avogadro’s Law

According to Avogadro’s law, if the gas is an ideal gas, the system has the same number of molecules. The law also indicates that if the volume of gases is equal, the number of molecules will be the same as the ideal gas only when the volume is identical. This statement can be stated numerically as

V₁ / n₁ = V₂ / n₂

Where V denotes the volume of an ideal gas and n denotes the number of gas molecules in the preceding equation. The temperature in this location is measured on the Kelvin scale. Because the volume here is constant, the graph for Gay-Law Lussac’s is referred to as an isochore.

Avogadro’s Law

Amedeo Avogadro merged the conclusions of Dalton’s Atomic Theory with Gay Lussac’s Law in 1811 to create the Avogadro’s Law, which is an essential Gas law. Avogadro’s law states that under constant temperature and pressure, the volume of all gases equals an equal number of molecules. In other words, under constant temperature and pressure, the volume of any gas is directly proportional to the number of molecules in that gas.

The previous gas laws provide an overview of the many properties of gases at various temperatures, pressures, volumes, and masses. These laws may appear insignificant, but they play a significant role in our daily lives. The difference in gaseous behaviour under altered conditions can affect everything from respiration to hot air balloons and automobile tyres.

Combined Gas Law

The combined gas law, also known as a general gas equation, is formed by merging three gas laws: Charle’s law, Boyle’s law, and Gay-Lussac law. The law describes the relationship between temperature, volume, and pressure for a given amount of gas. If we want to compare the same gas in different situations, the law can be expressed as follows:

(P₁ * V₁) / T₁ = (P_{2 *} V₂) / T₂

Ideal Gas Law

The ideal gas law, like the combined gas law, is a synthesis of four separate gas laws. Avogadro’s law is applied here, and the combined gas law is transformed into the ideal gas law. This law connects four different variables: pressure, volume, the number of moles or molecules, and temperature. Essentially, the ideal gas law describes the relationship between the four factors listed above. The ideal gas law is stated mathematically as;

PV=nRT

where, V = volume of gas, T = temperature of the gas, P = pressure of the gas, R = universal gas constant and n denotes the number of moles.

Check: Behavior of Gas Molecules

Gas Law Formula Table

Gas Law	Formula	Description
Ideal Gas Law	PV = nRT	Relates pressure, volume, temperature, and number of moles of gas.
Avogadro’s Law	V / n = constant	As the amount of gas increases, so does its volume.
Boyle’s Law	P1V1 = P2V2	At constant temperature, increasing pressure decreases volume.
Charles’s Law	V1/T1 = V2/T2	At constant pressure, volume is directly proportional to temperature.
Gay-Lussac Law	P1/T1 = P2/T2	At constant volume, pressure increases with temperature.

Check:

• Kinetic Theory of Gases
• Gay-Lussac’s Law

Problems Related to Gas Law

Question 1: What are gas laws?

Answer:

A gas’s state variables, such as pressure, volume, and temperature, reveal its true nature. As a result, gas laws are relationships between these variables.

Question 2: What is the effect of temperature on a gas?

Answer:

The state variables of a gas, such as pressure, volume, and temperature, reflect the true nature of the gas. As a result, gas laws are based on the interactions of these variables.

Question 3: What is Avogadro’s law?

Answer:

According to Avogadro’s law, if the gas is an ideal gas, the system has the same number of molecules. The law also indicates that if the volume of gases is equal, the number of molecules will be the same as the ideal gas only when the volume is identical.

Question 4: Name the four variables in ideal gas law?

Answer:

The four distinct variables are pressure, volume, the number of moles or molecules, and temperature.

Question 5: What is the relation between temperature and volume in gases?

Answer:

When the temperature increases, the volume increases, and when the temperature falls, the volume falls. Thus, they are directly proportional to each other.

Application of Gas Laws

• When the physical conditions of the environment change, the behaviour of gas particles deviates from their regular behaviour. The numerous laws known as gas law can be used to investigate these changes in gas behaviour. 
• The gas laws have been around for a long time, and they greatly assist scientists in determining quantities, pressure, volume, and temperature when it comes to gas. 
• Furthermore, the gas law, as well as newer variants, are used in a variety of practical applications using gas. For example, measurements of respiratory gases, tidal volume, and vital capacity, among other things, are taken at room temperature, despite the fact that these exchanges occur in the body at 37 degrees Celsius. 
• The law is also frequently utilised in thermodynamics and fluid dynamics. It can be employed in weather prediction systems.

Check: Applications of Ideal Gas Law

Characteristics of an Ideal Gas

• Ideal gases exhibit constant and random linear motion.
• The volume occupied by the particles of an ideal gas is minimal due to their small size.
• There are no intermolecular forces between gas particles; they only undergo elastic collisions with each other and the container walls.
• The kinetic energy of gas particles is directly proportional to their absolute temperature.
• Ideal gases consist of numerous identical particles (atoms or molecules) that are considered perfectly hard, small spheres.
• The volume of individual gas molecules is negligible compared to the space between them, leading to their treatment as point masses in calculations.

Check:

• Derivation of Ideal Gas Equation
• Gas Pressure Formula

Gas Laws – FAQs

What are the basic Gas Laws?

• Boyle’s Law relates pressure and volume of a gas, showing they are inversely proportional at constant temperature.
• Charles’s Law links the volume of a gas to its temperature, demonstrating that volume is directly proportional to temperature when pressure is constant.
• Gay-Lussac’s Law associates the pressure of a gas with its temperature, indicating that pressure is directly proportional to temperature at constant volume.
• Avogadro’s Law states that equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
• The Combined Gas Law combines these relationships, and the Ideal Gas Law further integrates these with the mole concept to relate pressure, volume, temperature, and the number of moles of gas​.

How do real gases differ from ideal gases?

Real gases differ from ideal gases primarily in how they respond under high pressures and low temperatures. The compressibility factor (Z) indicates this deviation, where Z=1 for ideal gases but varies for real gases depending on conditions​.

Can you provide examples of real-life applications of Boyle’s Law?

Boyle’s Law can be observed in action with syringes and human lungs, where changes in volume inside the syringe or lungs lead to inverse changes in pressure, allowing for drawing in or expelling substances​.

How is Charles’s Law applied practically?

Charles’s Law finds practical applications in scenarios where gases need to expand or contract due to temperature changes, such as in hot air balloons or in temperature control systems within sealed environments​.

What is Avogadro’s Law and its significance in chemistry?

Avogadro’s Law is pivotal for understanding that equal volumes of different gases contain the same number of particles when held at the same temperature and pressure. This principle is fundamental in determining molecular weights and in stoichiometric calculations in chemistry