Physics

Thermodynamics and Gas Laws

616 Questions

Thermodynamics and gas laws questions test the understanding of ideal gas behavior, work done during thermodynamic processes, and specific heat ratios. Key areas include isothermal, adiabatic, and isobaric expansions along with real gas deviations. These mathematical physics concepts are standard in engineering and general science competitive exams.

Ideal gas equationIsothermal and adiabatic processesThermodynamic workGas kinetic theoryReal gas behavior

Thermodynamics and Gas Laws Questions

Multiple choice

At what temperature will the root mean square velocity of hydrogen be double of its value at S.T.P. , pressure remaining constant?

  1. 819oC

  2. 1092oC

  3. 1365oC

  4. 819oC

  5. 273oC
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 Let V1 be the r.m.s. velocity at S.T.P. and  V2 be the r.m.s. velocity at unknown temperature T2. Here, T1 = 273 K T2 =?  (V2 / V1 )= 2 V2 rms = 3KT/m We know, v2 ∝ T ∴ V12 / V22 = T1/T2  T2 = T1 (V2 / V1 )2       = 273 x 22       = 273 x 4       = 1092 K T2 = 1092 - 273     =  8190C

Multiple choice

The specific heat of argon at constant volume is 0.075 kcal/kg K. Calculate the atomic weight. [Given: R = 2cal/mol K]

  1. 40 gm/mole

  2. 53.33 gm/mole

  3. 17.77 gm/mole

  4. 0.225 gm/mole

  5. 0.1 gm/mole
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As argon is monatomic, its molar specific heat at constant volume will be Cv= (3/2)R = (3/2)2 = 3 cal/mol K Now as Cv = Mcv with Cv = 0.075 cal/gk              3 = M x 0.075          Mw = 3 / 0.075                =  40 gm/mole

Multiple choice

A gram molecule of a gas is allowed to expand adiabatically at 327oC till the volume is four times the initial volume. Calculate the amount of heat absorbed. J = 4.2 x 107 ergs/cal, R = 8.31 x 107 ergs/gm mole oC and γ = 1.5

  1. 1187.14 cal

  2. 20941.2 x 1014 cal

  3. 593.57 cal

  4. 2374.28 cal

  5. 3561.42 cal
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 T2 = T1 (V1/ V2)γ -1 = 300K = 270C Hence work done, W = {R/(γ - 1)}( T1 – T2)      = {8.31 x 107/(1.5 - 1)} x 300      = 4986  x 107 Heat absorbed, H = W/J     = 4986 x 107/4.2 x 107    = 1187.14 cal

Multiple choice

Which of the following is a wrong statement regarding the postulates of kinetic theory of gases?

  1. The molecular density of the gas remains unchanged throughout the gas.

  2. The molecules of gases possess potential energy & kinetic energy.

  3. The molecules of a gas obey Newton's laws of motion.

  4. The collisions are perfectly elastic in nature.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The molecules of gases do not exert any force of attraction or repulsion on each other, except at the time of collision. Thus, the molecules do not have any potential energy. Their energy is only kinetic energy.

Multiple choice

During isothermal expansion of ideal gas its

  1. internal energy increases

  2. enthalpy increases

  3. enthalpy remains constant

  4. enthalpy reduces to zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Enthalpy is a thermodynamic function of a system. It is equivalent to the sum of the internal energy of the system plus the product of its volume multiplied by the pressure exerted on it by its surroundings. Since heat is absorbed from the surroundings therefore the enthalpy of the ideal gas increases.

Multiple choice

In case of an ideal gas, Joule-Thomson effect is ______.

  1. zero

  2. positive

  3. negative

  4. infinite
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Joule-Thomson effect is the temperature change of a gas when it expands through a porous plug without doing external work and with no heat transfer. For an ideal gas, there are no intermolecular forces, so this effect equals zero.

Multiple choice

The kinetic theory of gases predicts that at a given temperature-

  1. All the molecules in a gas have the same average speed

  2. All the molecules in a gas have the same average energy

  3. Lighter gas molecules have higher average energies than heavy gas molecules

  4. Lighter gas molecules have lower average energies than heavy gas molecules
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Kinetic theory states that at a given temperature, all gas molecules have the same average kinetic energy (KE_avg = 3/2 kT). Lighter molecules move faster but their average energy equals heavier molecules' average energy. Speeds follow Maxwell-Boltzmann distribution.

Multiple choice

Which of the following statements are TRUE?

  1. The protecting power of lyophilic colloidal sol is expressed in terms of gold number.
  2. Rate of physical adsorption increase with decrease in temperature.
  3. In Freundlich Adsorption isotherm, the value of 1/n is 0 in case of physical adsorption and 1 in case of chemisorptions.
  4. In Langmuir's model of adsorption of a gas on a solid surface the mass of gas striking a given area of surface is independent of the pressure of the gas. Select the correct answer.

  1. only 1 and 2

  2. 1, 2 and 3

  3. 1 and 4

  4. 2 and 3

  5. 3 and 4

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Only statement 1 and 2 are true statements. The protecting power of lyophilic colloidal sol is expressed in terms of gold number. Rate of physical adsorption increase with decrease in temperature.

Multiple choice

If the vapour pressure at two temperatures of a solid phase in equilibrium with its liquid phase are known, then the latent heat of fusion can be calculated by

  1. Maxwell's equations

  2. Van der Waals equation

  3. Nernst heat theorem

  4. Clayperon-Claussius equation

  5. Gauss's law
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The Claussius-Clayperon equation allows us to estimate the vapour pressure at another temperature, if the vapour pressure is known at some temperature, and if the enthalpy of vaporisation is known.