Ideal Gas Law and Real Gas Law

Difference Between Ideal Gas Law and Real Gas Law

A brief introduction to Ideal Gas Law and Real Gas Law

The Ideal Gas Law and Real Gas Law are two fundamental theories in thermodynamics as well as gas behavior, providing insight into the interaction among basic properties of gases such as volume, pressure temperature pressure and amount of molecules present. Though both laws aim to define gas behavior they differ considerably in their basic assumptions and precision in depicting actual conditions.

Ideal Gas Law (or PV = nRT, where P represents pressure, V refers to the volume of gas, mole count in moles is represented by number n and R is constant while T represents temperature).

This equation relies on several assumptions related to gas particles being small volume without exerting intermolecular force on each other and collisions being elastic; such assumptions allow this formula to work optimally under lower pressure and higher temperature conditions where optimal behavior of gases occurs; it makes calculations easier and produces fairly accurate results across various gases.

Real Gas Law takes into account deviations from the ideal behavior of real gases at extreme pressures or low temperatures when intermolecular forces become significant. Real Gas Law utilizes corrections to account for these variations, often employing equations like the van der Waals equation to do so.

These corrections are determined by how large molecules are (term “a'”) as well as intermolecular forces (term “b”) and other variables of the Ideal Gas Law equation. By including these corrections into its equation, Real Gas Law becomes the more precise representation of gas behavior across more situations than Ideal Gas Law can do.

Understanding the differences between Ideal Gas Law and Real Gas Law is critical in many practical and scientific applications, from engineering operations to ecological research. By understanding their respective assumptions and limitations, engineers and scientists can more accurately predict and model gas’s behavior in various circumstances; from industrial operations to ecological research. Researchers can then select an approach suitable for their system analysis while making informed choices.

Importance of understanding ideal gas law and real gas law

Understanding the ideal gas law and real gas law is crucial for several reasons:

1. Anticipating Gas Behavior: Laws provide the framework for understanding and forecasting the behavior of gases under various conditions. They help in determining relationships among important variables like temperature, volume, pressure, and quantity of gas.

2. Practical Applications: Gas laws have multiple practical uses across numerous fields, such as physics, chemistry engineering, and environmental science. They’re utilized for designing and operating systems that utilize gases like storage of gas for transportation or industrial processes.

3. Ideal Gas Law: The Ideal Gas Law serves as an essential model to demonstrate how gases behave idealistically, meaning they follow mathematical rules without intermolecular forces or volumetric increases between gas particles. Knowing this law makes calculations and scenarios that closely resemble this idealized behavior much simpler.

4. Real Gas Laws: Real gas laws differ significantly from their ideal counterparts under certain conditions, including extreme pressures and temperatures. Using equations of state like Van der Waals’ equation to describe them takes into account factors like intermolecular forces as well as finite quantities of particles; understanding these laws accurately is vital for making accurate calculations and forecasts in real-life scenarios.

5. Low-Temperature and High-Pressure Conditions: Under extreme temperatures or pressures, ideal gas assumptions break down and the actual behavior of gas can become apparent – examples being cryogenics used in industrial processes as well as studies conducted under extreme conditions. Real gas laws provide accurate explanations for its behavior under such circumstances.

6. Laboratory and Experimental Work: In laboratories, understanding the laws of gas can assist researchers in conducting experiments, analyzing data, interpreting their results, and creating controls and manipulations that provide precise measurement and observation. This allows them to make measurements with more accuracy while performing observations more reliably.

7. Safety Considerations: Understanding gas laws is vital to maintaining safe working environments when handling or working with gas. Learning about how changes in temperature, pressure, or volume affect gas behavior will assist you in avoiding accidents as well as maintaining an ideal working environment.

8. Additional Research and Scientific Advances: Gas laws remain at the core of research efforts, with researchers exploring and improving how gas behavior is understood. By understanding ideal and true gas laws, scientists can gain more insight into areas like material energy storage, materials science, and atmospheric Chemistry – furthering understanding in each.

An understanding of both the perfect gas law and real gas law is fundamental for forecasting gas behavior, applying its principles in real-world situations, taking account of deviations from the ideal, and guaranteeing safety. It serves as the cornerstone for accurate calculations, experiments work, and advancements across various fields.

Ideal Gas Law

The perfect gas law, or general gas equation, is one of the fundamental concepts of thermodynamics and gas behavior. It describes the relationships among volume, pressure, temperature, amount of gas in an environment, and overall system performance.

A perfect gas law can be expressed mathematically:

PV = nRT


  • P represents the gas pressure within the system (typically expressed in Pascals or Atmospheres).
  • V stands for volume (typically measured in cubic meters or liters).
  • n denotes the amount of gas, commonly expressed in moles.
  • The ideal gas constant (IGC) is a constant determined by the units being used in the calculation.
  • T is the absolute temperature in Kelvin.
Ideal Gas Law
Figure 01: Ideal Gas Law

Key aspects of the ideal gas law:

1. Assumptions: The ideal gas law assumes that the gas being studied behaves ideally, meaning it follows certain assumptions. These assumptions include:

  • The gas particles are considered point-like, having negligible volume.
  • There are no intermolecular forces between gas particles.
  • The collisions between gas particles and with the container walls are perfectly elastic.
  • Gas particles move randomly throughout their study volume.

2. Relationship between Variables: A perfect gas law provides an inverse relationship between the volume, pressure, and temperature of the gas as well as its quantity in its container. According to this law, when temperature, volume of gas, and pressure remain the same and pressure increases, volume decreases (and vice versa). Also if both pressure and quantity of gas remain the same while temperature increases results in increased volume (and vice versa).

3. Applications and Versatility: Ideal Gas law is utilized across many engineering and scientific fields. It can be utilized to study and predict gas behavior in systems like chemical reactions, mixtures of gas, or phase equilibrium; additionally, it enables calculations that identify unknown variables where others already exist.

4. Limitations: A perfect gas law can be thought of as an approximation that holds in conditions in which all the assumptions for ideal behavior hold. As temperatures or pressure increase or intermolecular forces become significant, its accuracy diminishes; deviations should be taken into account, and alternative formulas like actual gas laws utilized.

Mastering the ideal gas law provides engineers and scientists with a framework for understanding gas behavior in various situations and making calculations accordingly. Furthermore, it helps develop predictions, design systems, and examine characteristics of molecules of gas molecules.

Real Gas Law

Real gas laws or equations of state for real gases provide a framework to explain their behavior which does not conform to those outlined by perfect gas laws. Real gas behaves differently from its ideal behavior when exposed to high pressures or temperatures due to factors like intermolecular forces and smaller spaces between particles; many equations have been proposed to account for these variations, with the Van der Waals equation of state being one such solution.

This equation of the Van der Waals state can be seen here:

(P + a(n/V)2)(V + Nb) = nRT


  • P denotes the pressure of the gas in which we’re discussing.
  •  V represents the volume of gas.
  • n is the amount of gasoline in moles.
  • R is the ideal gas constant.
  • T is used to indicate what temperature the gas has reached.

The Van der Waals equation introduces two correction factors:

  • The “a” term addresses intermolecular forces. Gas particles attract each other, so this term adjusts pressure by these attractive forces.
  • The “b” term accounts for small volumes of gas particles by altering the volume term to take account of particle sizes.
Real Gas Law
Figure 02: Real Gas Law

Real gasses may also be represented by several equations of state that apply specifically to them, including the Redlich-Kwong equation, the Soave-Redlich Kwong equation, and the Peng-Robinson equation. Each of these includes correction factors to account for any individual properties and characteristics unique to real gases.

Actual gas laws are important because of their ability to provide more precise estimates and descriptions of how gases behave when ideal gas assumptions fail, particularly at extreme pressures, low temperatures, or when dealing with intermolecular forces that exert strong forces between molecules.

Real-world gas laws allow greater understanding and calculations for real gas-based systems such as industrial processes, transportation of gas, or cryogenic applications. By considering effects such as intermolecular forces and finite volumes of particles present within gas molecules, real-world gas laws provide a more accurate picture of gas behavior than perfect gas laws do.

Comparison Chart of Ideal Gas Law and Real Gas Law

This chart compares the main differences between real gas law and the actual gas law:

Topics Ideal Gas Law Real Gas Law
Assumptions Assumes ideal gas behavior: point-like particles, no intermolecular forces, negligible gas particle volume. Considers deviations from the ideal behavior: consider intermolecular forces, as well as the finite volume of gas particles.
Mathematical Representation PV = nRT, where P represents pressure V is volume n is the quantity of gas and R, is the optimal gas constant, and T is temperature. Many equations of state including the Van der Waals equation Redlich Kwong equation, Soave-Redlich equation, or the Peng-Robinson equation with additional correction factors to account for irregular behavior.
Applicability Gases that can be used under optimal conditions, with minimal deviations from the ideal behavior. Most accurate when low pressures and temperatures. Gases that are not ideal under conditions, with significant deviations from the ideal behavior, for example, high temperatures or low pressures.
Accuracy Offers fairly precise predictions in ideal conditions, but gets less precise as gases diverge from their ideal behavior. Offers more precise descriptions and forecasts of gas’s behavior specifically when the conditions are not ideal and deviations from the ideal behavior can be significant.
Practical Use A lot of people use it for calculations and analysis under optimal conditions, where the ideal assumptions about gas behavior remain to be true. It is used in situations in which non-ideal behavior plays a crucial role, for example, gas transportation, industrial processes cryogenics, and the most extreme conditions for gas.

This chart of comparison summarizes the key differences between the perfect gas law as well as the actual gas law about their assumptions mathematical representation, precision, applicability, and practical application.

Applications and Examples

1. Gas Stoichiometry: This ideal gas law can be used to calculate the stoichiometry of gaseous reactions by correlating their amount and volume with chemical reactions that take place in them.

2. Gas Laws during Experiments: Best gas laws are employed during lab experiments that involve gas collection and measurement to help identify unknown variables or to verify experimental results.

3. Analyzing Gas Pressure: An accurate gas law can be used to calculate the pressure of a given volume of gas when its volume, temperature, and weight are known.

4. Gas Behavior in Engineering: Engineering professionals use the ideal gas law to design and understand gas-driven systems such as gas turbines, combustion engines, and HVAC units.

5. Gas Laws in Environmental Science: A gas law is a perfect model to utilize when conducting atmospheric research studies to gain more insights into the properties and behaviors of atmospheric gases.

Examples of Real Gas Law Applications:

1. Industrial Applications: Gas laws are utilized in industrial processes requiring gases, including gas liquefaction, storage of gases, and chemical reactions that take place under high pressures or temperatures.

2. Pipelines and Gas Transport and Pipelines: Real gas laws must be considered when designing and operating pipelines to transport gas, taking into account factors like pressure drop, compressibility, and gas behavior under different conditions.

3. Cryogenics: Understanding gas behavior at very low temperatures is of critical importance when dealing with cryogenic engineering, superconductivity, and storage at lower temperatures. This understanding can assist engineers when designing cryogenic equipment or superconductors.

4. Gas Mixtures: Gas laws can be utilized to analyze the behavior of non-ideal gas mixtures, especially in non-ideal circumstances where different gases interact with one another in unexpected ways.

5. High-Pressure Systems: Gas laws are utilized when analyzing and designing high-pressure equipment such as pressure vessels, gas storage tanks, and industrial processes that utilize high-pressure gases.

Remind yourself that both ideal gas laws and actual gas laws have applications across various engineering and scientific disciplines, with their exact selection largely depending on what the application or situation requires for accuracy and requirements.


Understanding both Ideal Gas Law and Real Gas Law is critical to comprehending gas behavior and making accurate predictions for various engineering and scientific research applications. Ideal gas laws serve as a basic model which assumes optimal behavior in certain circumstances, providing a simplified explanation for volume, pressure temperature, and amount of gas in certain environments. They offer an approachable way of explaining relationships among volume pressure temperature amount of gas produced and the amount released into the environment.

While ideal gas laws are useful when gases closely follow their ideal behavior at lower pressures and temperatures; their accuracy decreases significantly when intermolecular forces or particle sizes have a significant bearing on gas behavior.