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JEE Main Unit 3A1: Gas Laws & Kinetic Molecular Theory — practice questions

Explore 6 free Unit 3A1: Gas Laws & Kinetic Molecular Theory questions in JEE Main Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Unit 3A1: Gas Laws & Kinetic Molecular Theory questions and exercises with answers

Showing questions 1–6 of 6.

The ideal gas equation of state is:Read the answer and worked solution →Boyle's law for a fixed amount of gas at constant temperature states that:Read the answer and worked solution →Charles's law for a fixed amount of gas at constant pressure states that:Read the answer and worked solution →The compressibility factor $Z$ of a gas is defined as $Z = \dfrac{PV}{nRT}$. For an ideal gas, $Z$ equals:Read the answer and worked solution →Above what temperature can a gas not be liquefied by pressure alone, no matter how much pressure is applied?Read the answer and worked solution →Crystalline solids are characterised by:Read the answer and worked solution →

Worked practice questions

The ideal gas equation of state is:

  1. $PV = RT$
  2. $PV = nRT$
  3. $P + V = nRT$
  4. $\dfrac{P}{V} = nRT$
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Correct answer: B. $PV = nRT$

Ideal gas law: $PV = nRT$, where $P$ is pressure, $V$ is volume, $n$ is moles, $R$ is the universal gas constant ($8.314$ J/(mol·K) or $0.0821$ L·atm/(mol·K)), and $T$ is absolute temperature in Kelvin. This equation combines Boyle's law ($PV =$ const at fixed $T, n$), Charles's law ($V/T =$ const at fixed $P, n$), and Avogadro's hypothesis ($V/n =$ const at fixed $T, P$) into one statement.

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Boyle's law for a fixed amount of gas at constant temperature states that:

  1. Pressure is directly proportional to volume
  2. $P^2 V = $ constant
  3. Pressure is inversely proportional to volume
  4. Volume is independent of pressure
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Correct answer: C. Pressure is inversely proportional to volume

Boyle's law: at fixed $T$ and $n$, $PV = $ constant, so $P \propto 1/V$. Squeeze a gas into half the volume at constant temperature and its pressure doubles. The $P$-$V$ curve at fixed $T$ is a hyperbola called an isotherm. Option A is the opposite (direct proportion), which would mean compressing a gas reduces its pressure — physically absurd.

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Charles's law for a fixed amount of gas at constant pressure states that:

  1. $V \propto T^2$
  2. $V$ is independent of $T$
  3. $V \propto T$ (Kelvin)
  4. $V \propto 1/T$
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Correct answer: C. $V \propto T$ (Kelvin)

Charles's law: at fixed $P$ and $n$, volume is directly proportional to absolute temperature ($T$ in Kelvin): $V/T = $ constant. Double the Kelvin temperature, double the volume. The key subtlety is that $T$ must be in Kelvin, not Celsius — Charles's law fails badly if you use Celsius (a gas at $0°$C has nonzero volume). Graphically, $V$ vs $T$ (Kelvin) is a straight line passing through the origin.

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