Q.Write the ideal gas equation.

Showing the 12 most recent of 26 on this concept.

1. CBSE 2026Set ANNUAL1 markMCQ
   Q.Which of the following is the value of the universal gas constant (R)?

   (a) 8.13 J mol^-1 K^-1

   (b) 8.31 J mol^-1 K^-1

   (c) 8.31 J^-1 mol^-1 K^-1

   (d) 8.13 J^-1 mol^-1 K^-1

   ›Reveal solutionSolution

   The universal gas constant R = 8.31 J mol⁻¹ K⁻¹ (commonly rounded from 8.314 J mol⁻¹ K⁻¹).

   From the ideal gas equation PV = nRT, R is the constant of proportionality connecting pressure, volume, amount of substance, and temperature, and is the same for all ideal gases (hence 'universal'). Its measured value is R = 8.314 J mol⁻¹ K⁻¹ ≈ 8.31 J mol⁻¹ K⁻¹ (equivalently ≈ 1.987 cal mol⁻¹ K⁻¹, or 0.0821 L·atm mol⁻¹ K⁻¹ in other unit systems). Options (c) …

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2. CBSE 2026Set ANNUAL1 mark
   Q.Write the ideal gas equation.

   ›Reveal solutionSolution

   The ideal gas equation is PV = nRT.

   Combining Boyle's law (P ∝ 1/V at constant T), Charles's law (V ∝ T at constant P), and Avogadro's law (V ∝ n at constant P, T) gives the single equation of state for an ideal gas: PV = nRT, where P is the pressure, V the volume, n the number of moles of gas, R the universal gas constant (8.31 J mol⁻¹ K⁻¹), and T the absolute temperature (i …

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3. CBSE 2026Set ANNUAL1 markMCQ
   Q.According to ideal gas equation:

   (a) PV = μRT

   (b) PV^r = Constant

   (c) P^rV = RT

   (d) PV = μR/T

   ›Reveal solutionSolution

   The ideal gas equation of state is PV = mu*RT, connecting pressure, volume, the number of moles, the universal gas constant, and absolute temperature.

   The ideal gas equation is derived by combining Boyle's law (PV = constant at constant T), Charles's law (V/T = constant at constant P), and Avogadro's law (V proportional to number of moles at constant P and T) into a single equation of state:

   PV = muRT

   where:

   P = pressure of the gas

   V = volume of the gas

   mu = number of moles of gas

   R = universal gas constant (8.314 J/mol K)

   T = absolute temperature (in kelvin)

   …

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4. CBSE 2026Set ANNUAL1 markMCQ
   Q.If the internal energy of an ideal gas U and volume V are doubled, then the pressure:

   (a) halves

   (b) doubles

   (c) increases four times

   (d) remains same

   ›Reveal solutionSolution

   Since U is proportional to T for an ideal gas, doubling U doubles T; combined with V also doubling, the pressure P = mu*RT/V is unchanged because the factor of 2 in T is exactly cancelled by the factor of 2 in V.

   For an ideal gas (fixed number of moles mu), the internal energy is

   U = (f/2)muR*T

   where f is the number of degrees of freedom. This shows U is directly proportional to the absolute temperature T.

   Step 1: If U becomes 2U, then since U is proportional to T, the temperature must also become 2T (with mu and f unchanged).

   Step 2: The ideal gas equation is PV = muRT, so P = muRT/V.

   Step 3: With the new values T' = 2T and V' = 2V,

   P' = muR(2T)/(2V) = muRT/V = P (unchanged)

   …

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5. CBSE 2025Set ANNUAL1 markMCQ
   Q.The dimension of universal gas constant R is the same as that of (A) energy (B) heat capacity (C) molar heat capacity (D) temperature

   ›Reveal solutionSolution

   The universal gas constant R has the same dimension as molar heat capacity.

   From the ideal gas law $PV = nRT$:

   $R = \dfrac{PV}{nT}$

   Dimensionally, $[PV] =$ energy $= [ML^2T^{-2}]$, so:

   $[R] = \dfrac{[ML^2T^{-2}]}{[\text{mol}][K]}$

   …

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6. CBSE 2025Set ANNUAL1 markMCQ
   Q.The graph between Volume and Temperature in Charles' law is:

   (a) a straight line

   (b) an ellipse

   (c) a parabola

   (d) a circle

   ›Reveal solutionSolution

   Charles' Law (V proportional to T at constant pressure) gives a straight-line V-T graph passing through the origin, when temperature is measured on the absolute (Kelvin) scale.

   Charles' Law: for a fixed mass of gas held at constant pressure, V/T = constant, or equivalently V = (constant) x T.

   This is exactly the equation of a straight line y = mx through the origin, with V playing the role of y, T playing the role of x, and the constant playing the role of the slope m.

   …

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7. CBSE 2025Set hz1 markMCQ
   Q.Two vessels A and B of the same size are at the same temperature, one of them holds 1Kg of H2 gas and the other hold 1Kg of N2 gas. Which of the vessels contains more molecules?

   (a) A only

   (b) B only

   (c) Both

   (a) and

   (b)

   (d) None of them

   ›Reveal solutionSolution

   Number of molecules = (mass / molar mass) x Avogadro's number. Since H2 has a much smaller molar mass than N2, 1 kg of H2 contains many more molecules than 1 kg of N2, so vessel A (H2) has more molecules.

   The number of molecules in a sample is N = n x N_A, where n = (given mass)/(molar mass) is the number of moles and N_A = 6.022 x 10^23 /mol is Avogadro's number.

   For vessel A, holding 1 kg = 1000 g of H2 (molar mass = 2 g/mol):

   n(H2) = 1000/2 = 500 mol

   N(H2) = 500 x N_A

   For vessel B, holding 1 kg = 1000 g of N2 (molar mass = 28 g/mol):

   n(N2) = 1000/28 approx 35.7 mol

   N(N2) approx 35.7 x N_A

   …

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8. CBSE 2025Set ANNUAL1 markMCQ
   Q.For an ideal gas, $PV = XT$, where $X$ is a constant, $X$ must be proportional to

   (a) mass of the gas molecule

   (b) absolute temperature

   (c) number of gas molecules in the vessel

   (d) kinetic energy of the gas.

   ›Reveal solutionSolution

   The ideal gas equation is $PV=nRT$, where $n$ is the number of moles of gas and $R$ is the universal gas constant (a true constant, same for all gases).

   Comparing the given equation $PV=XT$ with $PV=nRT$ term by term:

   $X = nR$

   …

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9. CBSE 2024Set ANNUAL1 markMCQ
   Q.Volume of a given mass of gas at constant pressure is (A) inversely proportional to absolute temperature (B) proportional to absolute temperature (C) proportional to temperature (D) inversely proportional to temperature

   ›Reveal solutionSolution

   By Charles's law, $V\propto T$ (absolute temperature) at constant pressure.

   For an ideal gas, $PV=nRT$. At constant pressure and fixed amount of gas ($n$), $V=\dfrac{nR}{P}T$, i.e. $V\propto T$ where $T$ must be the absolute (Kelvin) temperature — this direct proportionali …

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10. CBSE 2024Set SET-AP55001 mark
    Q.What is Boyle's law?

    ›Reveal solutionSolution

    Boyle's law states that for a fixed mass of gas at constant temperature, pressure is inversely proportional to volume: PV = constant.

    Formally, for a fixed quantity (mass/moles) of an ideal gas held at constant temperature T:

    P ∝ 1/V ⟹ PV = constant

    …

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11. CBSE 2024Set SET-NDP60001 markMCQ
    Q.What is the relationship between pressure P1 & P2 in the given V-T diagram?

    (a) P1 > P2

    (b) P2 > P1

    (c) P1 = P2

    (d) Cannot be determined

    ›Reveal solutionSolution

    On an isochoric-family V–T plot, a steeper line means a lower pressure, so the steeper line (P2, closer to the V-axis) has the smaller pressure, making $P_1 > P_2$.

    For $n$ moles of an ideal gas, $PV = nRT$, so at fixed pressure $P$ and fixed amount $n$,

    $V = \left(\dfrac{nR}{P}\right) T$

    This is the equation of a straight line through the origin on a V–T graph, with slope $= nR/P$. Since $n$ and $R$ are the same for both lines, the slope is inversely proportional to the pressure: a larger slope (a line closer to the V-axis, i.e. rising more steeply) corresponds to a smaller pressure, and a smaller slope (a line closer to the T-axis, i.e. flatter) corresponds to a larger pressure.

    …

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12. CBSE 2024Set ANNUAL1 mark
    Q.When do the real gases obey more correctly to the gas equation $PV = nRT$?

    ›Reveal solutionSolution

    The ideal-gas assumptions (negligible molecular size and negligible intermolecular forces) hold best when a real gas is at low pressure and high temperature.

    The ideal gas equation $PV=nRT$ is derived assuming that gas molecules have negligible volume compared to the container and exert no forces on each other except during brief elastic collisions. Real gas molecules do have finite size and do interact through intermolecular forces, so real gases deviate from $PV=nRT$, especially at high pressure (molecules packed close together, their own volume becomes significant) and low temperature (molecules move slowly, so intermolecular attractive forces become significant, even causing condensation).

    …

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