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

Directions: Carry One Mark Each.

An air-standard diesel cycle consists of the following processes:

1–2: Air is compressed isentropically. 2–3: Heat is added at constant pressure. 3–4: Air expands isentropically to the original volume. 4–1: Heat is rejected at constant volume. If $\gamma$ and T respectively denote the specific heat ratio and temperature, then the efficiency of the cycle is
  1. $1-\frac{T_4-T_1}{T_3-T_2}$
  2. $1-\frac{T_4-T_1}{\gamma(T_3-T_2)}$
  3. $1-\frac{\gamma(T_4-T_1)}{T_3-T_2}$
  4. $1-\frac{T_4-T_1}{(\gamma-1)(T_3-T_2)}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For an air-standard diesel cycle,

Multiple choice

In an experimental set-up, air flows between two stations P and Q adiabatically. The direction of flow depends on the pressure and temperature conditions maintained at P and Q. The conditions at station P are 150 kPa and 350 K. The temperature at station Q is 300 K. The following are the properties and relations pertaining to air: Specific heat at constant pressure, Cp = 1.005 kJ/kgK; Specific heat at constant volume, Cv = 0.718 kJ/kgK; Characteristic gas constant, R = 0.287 kJ/kgK Enthalpy, h = cp T Internal energy, u = Cv T

If the air has to flow from station P to station Q, the maximum possible value of pressure in kPa at station Q is close to

  1. 50

  2. 87

  3. 128

  4. 150
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

A compressor undergoes a reversible, steady flow process. The gas at inlet and outlet of the compressor is designated as state 1 and state 2, respectively. Potential and kinetic energy changes are to be ignored. The following notations are used:

V = specific volume and P = pressure of the gas The specific work required to be supplied to the compressor for this gas compression process is
  1. $\int\limits_1^2 PdV$
  2. $\int\limits_1^2 VdP$

  3. V1(P2 – P1)

  4. – P2(V1 – V2)

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

Multiple choice

2 moles of oxygen are mixed adiabatically with another 2 moles of oxygen in mixing chamber, so that the final total pressure and temperature of the mixture becomes same as those of the individual constituents at their initial states. The universal gas constant is given as R. The change in entropy due to mixing, per mole of oxygen, is given by

  1. -R In 2

  2. 0

  3. R In 2

  4. R In 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$Given : T_1=T_2, p_1=p_2 \\ \text{Universal Gas constant=R}\\ \text{Here given oxygen ara mixed adiabatically } \\ So,\hspace{3cm}dQ=0 \\ \text{We know,}\hspace{2cm}ds=\frac{dQ}{T}=\frac{0}{T}=0$

Multiple choice

A gas expands in a frictionless piston–cylinder arrangement. The expansion process is very slow, and is resisted by an ambient pressure of 100 kPa. During the expansion process, the pressure of the system (gas) remains constant at kPa. The change in volume of the gas is 0.01 m3. The maximum amount of work that could be utilized from the above process is

  1. 0 kJ

  2. 1 kJ

  3. 2 kJ

  4. 3 kJ
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$Given : p_a=100kPa, p_s=3000kPa,\triangle v=0.01m^3 \\ \text{Net pressure work on the system,}\\ \hspace{4cm}p=p_s-p_a=300-100=200kPa $

Multiple choice

A rigid, insulated tank is initially evacuated. The tank is connected with a supply line through which air (assumed to be ideal gas with constant, specific heat) passes at 1 MPa, 3500C. A valve connected with the supply line is opened and the tank is charged with air until the final pressure inside the tank reaches 1 MPa. The final temperature inside the tank

  1. is greater than 3500C

  2. is less than 3500C

  3. is equal to 3500C

  4. may be greater than, less than, or equal to 350C, depending on the volume of the tank
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice

A balloon containing an ideal gas is initially kept in an evacuated and insulated room. The balloon ruptures and the gas fills up the entire room. Which one of the following statements is TRUE at the end of the above process?

  1. The internal energy of the gas decreases from its initial value, but the enthalpy remains constant.

  2. The internal energy of the gas increases from its initial value, but the enthalpy remains constant.

  3. Both internal energy and enthalpy of the gas remain constant.

  4. Both internal energy and enthalpy of the gas increase.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\text{We know enthalpy,}\\ \hspace{3.4cm}h=U+pv \hspace{4cm}...(i)\\ Where,\hspace{2cm}U=\text{Internal energy}$