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What is a Real Gas (chemistry)?
Grade Level:
Class 8
Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics
Definition
What is it?
A real gas is any gas that exists in the real world and does not perfectly follow the ideal gas laws. Unlike ideal gases, real gases have particles with actual volume and experience attractive or repulsive forces between them, especially at high pressures or low temperatures.
Simple Example
Quick Example
Imagine you have a big bag of puffed rice (kurkure). If you think of each puffed rice as a gas particle, an ideal gas would be like tiny, invisible rice grains that don't take up any space and never touch each other. A real gas is like the actual puffed rice – each piece has its own size, and they can bump into each other or even stick together a little, especially if you squeeze them into a small bag.
Worked Example
Step-by-Step
Let's say we have 1 mole of a gas at a certain temperature and pressure. We want to see how its volume differs from an ideal gas.
---1. For an ideal gas, we use the Ideal Gas Law: PV = nRT. Let P = 10 atm, T = 300 K, n = 1 mole, and R = 0.0821 L.atm/(mol.K).
---2. Calculate the ideal volume (V_ideal): V_ideal = nRT/P = (1 * 0.0821 * 300) / 10 = 2.463 L.
---3. Now, consider a real gas like Carbon Dioxide (CO2). For CO2, we use the van der Waals equation: (P + a(n/V)^2)(V - nb) = nRT. Here, 'a' accounts for intermolecular forces and 'b' for particle volume.
---4. For CO2, a is approximately 3.59 L^2.atm/mol^2 and b is approximately 0.0427 L/mol.
---5. If we try to solve for V using the van der Waals equation with the same P, n, T, it's a bit complex without advanced tools, but we know V_real will be different from V_ideal. At high pressures, the 'nb' term (particle volume) becomes more important, making V_real larger than V_ideal. At low temperatures, the 'a' term (intermolecular forces) becomes more important, making V_real smaller than V_ideal due to particles pulling each other closer.
---6. For instance, at 10 atm and 300 K, the actual volume of 1 mole of CO2 is found to be slightly less than 2.463 L due to attractive forces, perhaps around 2.3 L (this is an approximation for illustration).
---Answer: The volume of the real gas (CO2) is different from the ideal gas volume, showing that real gases do not perfectly follow ideal gas behavior.
Why It Matters
Understanding real gases is crucial for engineers designing rockets and space vehicles, as fuel gases behave differently under extreme pressures and temperatures. It's also vital in chemical industries for processes involving gases, and for environmental scientists studying atmospheric gases and climate change. This knowledge helps create efficient engines, design better air conditioners, and understand industrial chemical reactions.
Common Mistakes
MISTAKE: Thinking that all gases behave ideally under all conditions. | CORRECTION: Real gases only behave *like* ideal gases under specific conditions: low pressure and high temperature.
MISTAKE: Believing real gas particles have no volume or no forces between them. | CORRECTION: Real gas particles *do* have a small but definite volume, and they *do* experience attractive and repulsive forces, especially when close together.
MISTAKE: Confusing ideal gas law with real gas equations. | CORRECTION: The Ideal Gas Law (PV=nRT) is a simplified model. For real gases, more complex equations like the van der Waals equation are needed to account for particle volume and intermolecular forces.
Practice Questions
Try It Yourself
QUESTION: What are two main differences between an ideal gas and a real gas? | ANSWER: 1. Ideal gas particles have no volume, real gas particles have volume. 2. Ideal gas particles have no intermolecular forces, real gas particles have intermolecular forces.
QUESTION: Under what two conditions do real gases behave most like ideal gases? | ANSWER: Real gases behave most like ideal gases at low pressure and high temperature.
QUESTION: Why would a gas in a deep-sea diving tank (under very high pressure) not behave ideally? | ANSWER: Under very high pressure, the gas particles are forced closer together. This means their own volume becomes significant compared to the container's volume, and the intermolecular forces become much stronger, causing deviations from ideal behavior.
MCQ
Quick Quiz
Which of the following statements is TRUE about real gases?
Their particles have no volume.
They always obey the Ideal Gas Law perfectly.
They experience intermolecular forces between particles.
They are only found in laboratories.
The Correct Answer Is:
C
Real gas particles have a definite volume and experience attractive/repulsive forces. They only approximate ideal behavior under specific conditions, and are found everywhere, not just labs.
Real World Connection
In the Real World
When you get an LPG cylinder delivered for your kitchen, the gas inside (liquefied petroleum gas) is a real gas. It's stored under high pressure, which is why it's a liquid. If it were an ideal gas, it would never liquefy, and you couldn't store so much cooking fuel in a small cylinder. Engineers at companies like Indian Oil or HP Gas use the principles of real gases to safely store and transport LPG.
Key Vocabulary
Key Terms
IDEAL GAS: A theoretical gas whose particles have no volume and no intermolecular forces | INTERMOLECULAR FORCES: Attractive or repulsive forces between gas particles | VAN DER WAALS EQUATION: A modified gas law used to describe the behavior of real gases | PRESSURE: Force applied perpendicular to the surface of an object per unit area | TEMPERATURE: A measure of the average kinetic energy of the particles in a substance.
What's Next
What to Learn Next
Great job learning about real gases! Next, you should explore the 'Ideal Gas Law' to understand the simplified model and then 'Kinetic Molecular Theory' to dive deeper into how gas particles move and interact. This will help you see the bigger picture of gas behavior.
