Physics

Thermodynamics and Gas Laws

626 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 chemistry matter in our surroundings diffusion in different states of matter properties of solids, liquid, and gas particle theory of matter

Compressibility is minimum in case of :

  1. solid.

  2. liquid.

  3. both (a) and (b).

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

In case of solid the inter-molecular force of attraction is very strong and inter-particle spaces are very small. So, it is very difficult to compress the solid.


Hence, the correct option is $A$.

Multiple choice chemistry matter in our surroundings diffusion in different states of matter properties of solids, liquid, and gas particle theory of matter

Which of these is a property of a gas.

  1. Has a fixed volume

  2. Has a fixed shape

  3. Doesn't have a fixed volume

  4. Doesn't have a fixed shape
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

The intermolecular forces in the case of gas are very very weak and hence the gas molecules are not at all held tightly. Thus a gas doesn't have a fixed shape at all.
Gases do not have a fixed volume too. It has the volume of the container in which it is kept.


Hence, the correct options are $C$ and $D$

Multiple choice chemistry matter in our surroundings diffusion in different states of matter properties of solids, liquid, and gas particle theory of matter

The translational kinetic energy of $10^{20}$ molecules of nitrogen at a certain temperature is $0.63$ J. The temperature is:

  1. $23^o$ C
  2. $31.3^o$ C
  3. $30.1^o$ C
  4. $43.3^o$ C
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$K.E=\dfrac{3}{2}N K _BT$


$N=10^{20}, K _B=1.38\times 10^{-23}$ Joule/, KE$=0.63$ J

$0.63=\dfrac{3}{2}\times 10\times 1.38\times 10^{-23}\times T$

$\Rightarrow T=\dfrac{0.63\times 2}{1.383}\times 10^3$

     $T=304.3$K

     $T=31.3^o$ C.

Hence, option $B$ is correct.

Multiple choice chemistry matter in our surroundings diffusion in different states of matter properties of solids, liquid, and gas particle theory of matter

At what temperature will the total translational kinetic energy of $0.30$ mole of He gas be the same as the total translational kinetic energy of $0.40$ mol of Ar at $400$ K?

  1. $533$ K
  2. $400$ K
  3. $300$ K
  4. $266$ K
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$n _1=0.30$ mol, $T _1=?$


$n _2=0.40$ mol, $T _2=400$ K

Using $n _1T _1=n _2T _2$

$0.3\times T _1=0.4\times T _2$

$T _1=\dfrac{4}{3}\times 400$

$=533$ K

Hence, option $A$ is correct.

Multiple choice chemistry matter in our surroundings diffusion in different states of matter properties of solids, liquid, and gas particle theory of matter

In which of the following conditions, the distance between the molecules of hydrogen gas would increase?

  1. increasing pressure on hydrogen contained in a closed container

  2. some hydrogen gas leaking out of the container

  3. increasing the volume of the container of hydrogen gas

  4. adding more hydrogen gas to the container without increasing the volume of the container
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

When hydrogen gas leaks out of the container, the molecules of the gas remaining in the container have more free space. Hence, distance between the gas molecules increases. By increasing the volume of the container also increases the distance between the molecules.

Multiple choice zoology respiratory system of human mechanism of respiration respiratory cycle breathing and exchange of gas

According to Boyle's law, the product of:.pressure and volume is a constant. Hence,

  1. if volume of lungs is increased, then pressure decreases proportionately

  2. if volume of lungs is increased, then pressure also increases proportionately

  3. if volume of lungs is increased, then pressure decreases disproportionately

  4. if volume of lungs is increased, then pressure remains the same.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
According to Boyle's law, the product of pressure and volume is a constant. Hence, if the volume of the lungs is increased, then pressure decreases proportionately.
So, the correct answer is 'if volume of lungs is increased, then pressure decreases proportionately'.
Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

At what temperature volume of an ideal gas at $0^oC$  becomes triple by keeping pressure constant

  1. $546^oC$
  2. $182^oC$
  3. $819^oC$
  4. $646^oC$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using Charles's Law (V1/T1 = V2/T2) at constant pressure, if V2 = 3*V1, then T2 = 3*T1. Given T1 = 0 C = 273 K, T2 = 3 * 273 = 819 K. Converting back to Celsius, 819 - 273 = 546 C.

Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

A container with insulating wall is divided into two equal parts by a partition fitted with a vaive.One part is filled with an ideal gas at pressure P and temperature T, whereas the other part is one part is  completely evacuated. If the valve is suddenly opened, the pressure and temperature of gas will be: 

  1. $P , \cfrac { T } { 2 }$
  2. $\cfrac { P } { 2 } , T$
  3. $\cfrac { P } { 2 } , \cfrac { T } { 2 }$
  4. $P , T$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is a free expansion (Joule expansion) into a vacuum. Since the walls are insulating (adiabatic) and no work is done (expansion against vacuum), the internal energy remains constant, meaning temperature T remains constant. The volume doubles, so by PV = nRT, the pressure must halve to P/2.

Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

The relation PV=RT can describe the behavior of a real gas at :

  1. high temperature and high pressure

  2. high temperature and low pressure

  3. low temperature and low pressure

  4. low temperature and high pressure
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

PV=RT is ideal gas equation and gases behave ideally only at high temperature and low pressure.
Therefore option(B).

Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

A real gas behaves as an ideal gas :

  1. at very low pressure and high temperature

  2. high pressure and low temperature

  3. high temperature and high pressure

  4. low pressure and low temperature
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Real gas obeys vanderwaals equation 
$\left( p+\dfrac { n^{ 2 }a }{ V^{ 2 } }  \right) \left( V-nb \right) =nRT$
at high temperature and low pressure
Van der waal equation becomes approximately PV=nRT
Hence gases behave ideally at high temperature and low pressure.
Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

The equation of state of a real gas can be expressed as $(P + \dfrac{a}{V _2}) (V - b) = cT$, where P is the pressure, V the volume, T the absolute temperature and a, b, c are constants. What are the dimensions of 'a'-

  1. $M^0 L^3 T^{-2}$
  2. $ M L^{-2} T^5$
  3. $M L^5 T{-2}$
  4. $M^0 L^3 T^0$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\left( {p + \frac{a}{{{V _2}}}} \right)\left( {v - b} \right) = cT$

$p$ is pressure, $V$ is volume and $T$ is temperature
$\begin{array}{l} p=\frac { F }{ A } =\frac { { ML{ T^{ -2 } } } }{ { { L^{ 2 } } } } =M{ L^{ -1 } }{ T^{ -2 } } \ V={ L^{ 3 } } \end{array}$
We cannot add or subtract quantities of different dimensions.
$\begin{array}{l} \therefore p=\frac { a }{ { { V^{ 2 } } } }  \ \Rightarrow a=\frac { p }{ { { V^{ 2 } } } } =\frac { { M{ L^{ -1 } }{ T^{ -2 } } } }{ { { { \left( { { L^{ 3 } } } \right)  }^{ 2 } } } } =M{ L^{ 5 } }{ T^{ -2 } } \end{array}$
Hence, Option $C$ is correct.

Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

Diatomic gas at pressure `P' and volume `V' is compressed adiabatically to 1/32 times the original volume. Then
the final pressure is

  1. P/32

  2. 32 P

  3. 128 P

  4. P/128
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For adiabatic processes, P * V^gamma = constant. For a diatomic gas, gamma = 1.4 or 7/5. P2 = P1 * (V1/V2)^gamma. Here V1/V2 = 32. P2 = P * (32)^(7/5) = P * (2^5)^(7/5) = P * 2^7 = 128P.

Multiple choice real gases van der-waal equation: equation of state for real gas kinetic theory of gases thermal physics physics

For a real gas, deviations from ideal gas behavior are maximum at 

  1. $-10^o C$ and $5.0 \,atm$
  2. $-10^o C$ and $2.0 \,atm$
  3. $0^o C$ and $1.0 \,atm$
  4. $100^o C$ and $2.0 \,atm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Real gases deviate most from ideal behavior at high pressures and low temperatures, where intermolecular forces and molecular volume become significant.