Example 1 · level 1
2 mol of an ideal gas is kept in a 20 L cylinder at 37°C. Find the pressure in kPa (correct to 2 decimal places). R = 8.314 J mol⁻¹ K⁻¹.
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- p = 2 × 8.314 × 310 ÷ 0.02 = 2,57,734 Pa = 257.73 kPa.
Answer: 257.73 kPa
CLASS 11–12 PHYSICS · KINETIC THEORY / THERMAL PROPERTIES
Ideal gas equation (pV = nRT)
pV = nRT with R = 8.314 J mol⁻¹ K⁻¹; use SI units (Pa, m³, K). 1 L = 10⁻³ m³; T(K) = t(°C) + 273.
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Worked examples
Example 2 · level 2
A gas cylinder of volume 50 L holds an ideal gas at 22.7 kPa and 0°C. How many moles of gas does it contain (correct to 2 decimal places)? R = 8.314 J mol⁻¹ K⁻¹.
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- n = 22,697.22 × 0.05 ÷ (8.314 × 273) = 0.5 mol.
Answer: 0.5 mol
Example 3 · level 3
A fixed mass of ideal gas at 150 kPa, 2 L and 400 K is changed to 3 L and 300 K. Find the new pressure in kPa (correct to 2 decimal places).
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- p₂ = 150 × 2 × 300 ÷ (400 × 3) = 75 kPa.
Answer: 75 kPa