A common and important question in Class 9 Chemistry (Matter in Our Surroundings) is: 'Suggest a method to liquefy atmospheric gases.' Understanding how matter changes its state is crucial for answering this.
Solid Carbon Dioxide (Dry Ice) is formed when CO₂ gas is placed under extreme pressure. Interestingly, when you release that pressure at room temperature, it turns straight back into a gas without melting into a liquid first (Sublimation).
To successfully liquefy an atmospheric gas (like Oxygen, Nitrogen, or Carbon Dioxide), you must simultaneously do two things:
The state of matter (solid, liquid, or gas) depends entirely on the distance between its particles and their kinetic energy.
Not always. Every gas has a 'Critical Temperature'. If the gas is hotter than its critical temperature, it doesn't matter how much pressure you apply; it will never turn into a liquid. You must cool it down first.
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