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ChemistryMediumClass 11

Ideal Gas Laws — Boyle's, Charles', Gay-Lussac's

States of Matter

4

JEE Qs

8%

Hard

60

min

Always convert temperature to Kelvin and ensure unit consistency for pressure and volume before applying any gas law formula.

🧮 Key Formulas

P1V1 = P2V2 (Boyle's Law, for constant n, T)
V1/T1 = V2/T2 (Charles' Law, for constant n, P)
P1/T1 = P2/T2 (Gay-Lussac's Law, for constant n, V)
P1V1/T1 = P2V2/T2 (Combined Gas Law, for constant n)
T(K) = T(°C) + 273.15

✅ Key Points for JEE

  • 1All gas laws are applicable only for a *fixed amount* (constant moles, n) of an ideal gas.
  • 2Temperature *must always* be expressed in Kelvin (absolute temperature) for all gas law calculations to be valid.
  • 3Ensure units of pressure and volume are consistent on both sides of the equation when applying the laws; use conversion factors if needed.
  • 4Understanding the graphical representations (e.g., P vs V, P vs 1/V, V vs T, P vs T) and how slopes/intercepts change is vital for conceptual questions.

⚠️ Common Mistakes

  • Failing to convert Celsius temperature to Kelvin before using any gas law formula.
  • Applying gas laws to situations where the amount of gas (n) is changing, leading to incorrect results.
  • Incorrectly identifying which variable (P, V, T) is held constant in a given problem statement.
  • Inconsistent use of units for pressure or volume within the same calculation, resulting in errors.

📝 Practice Questions

See all

Q49.A container of fixed volume contains a gas at 27∘C. To double the pressure of the gas, the temperature of gas should be raised to ______ ∘C.

2025·NumericalEasy

Q42.The ratio of vapour densities of two gases at the same temperature is 4 , then the ratio of r.m.s. velocities will 25 be: (1) 25 (2) 2 4 5 (3) 5 (4) 4 2 25

2025·MCQEasy

Q74.Some CO2 gas was kept in a sealed container at a pressure of 1 atm and at 273 K . This entire amount of CO2 gas was later passed through an aqueous solution of Ca(OH)2 . The excess unreacted Ca(OH)2 was later neutralized with 0.1 M of 40 mL HCl . If the volume of the sealed container of CO2 was x, then x is ________ cm3 (nearest integer). [Given : The entire amount of CO2( g) reacted with exactly half the initial amount of Ca(OH)2 present in the aqueous solution.] 2025 (22 Jan Shift 1) JEE Main Previous Year Paper

2025·NumericalHard

Q36.At 600 K, the root mean square (rms) speed of gas X (molar mass = 40) is equal to the most probable speed of gas Y at 90 K. The molar mass of the gas Y is _____ g mol–1 . (Nearest integer)

2023·NumericalMedium

Q53.At constant temperature, a gas is at a pressure of 940 . 3 mm Hg. The pressure at which its volume decreases by 40% is ______ mm Hg. (Nearest integer) +2 . 2 V +0 . 70 V -0 . 45 V 2 - ⟶ Fe3 + ⟶ Fe2 + ⟶ Fe0

2023·NumericalEasy

Q36. Three bulbs are filled with CH4, CO2 and Ne as shown in the picture. The bulbs are connected through pipes of zero volume. When the stopcocks are opened and the temperature is kept constant throughout, the pressure of the system is found to be______ atm. (Nearest integer).

2023·NumericalMedium

NCERT Chapters

  • Class 11 Chemistry Ch 5: States of Matter