🧪 Chemistry · States of Matter · NEET & JEE

A balloon filled with He gas at 1 atm and 300 K has volume 5 L. If it rises to an altitude where pressure is 0.5 atm and temperature drops to 250 K, what is its new volume, assuming ideal behavior?

Answer: 8.33 L.

A 4.17 L
B 8.33 L
C 10 L
D 2.5 L

Correct answer: B. 8.33 L

Explanation: Using combined gas law P1V1/T1 = P2V2/T2: (1 x 5)/300 = (0.5 x V2)/250, solving gives V2 = (5 x 250)/(300 x 0.5) = 8.33 L.

Graph of pressure versus volume for a fixed amount of gas at constant temperature: the curve falls steeply then flattens, a hyperbola showing pressure inversely proportional to volume.

Boyle's law: at constant temperature the pressure of a fixed mass of gas is inversely proportional to its volume (P ∝ 1/V), so the P–V plot is a hyperbola — halving the volume doubles the pressure. Image: Reginaprice2013, CC BY-SA 3.0, via Wikimedia Commons.

Concept context

Discover why gases expand to fill any container while liquids flow and solids hold their shape. Master the gas laws, the ideal gas equation, and the reasons real gases deviate from ideal behavior.

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A balloon filled with He gas at 1 atm and 300 K has volume 5 L. If it rises to an altitude where pressure is 0.5 atm and temperature drops to 250 K, what is its new volume, assuming ideal behavior?

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