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 physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A certain quantity of heat energy is given to a diatomic ideal gas which expands at constant pressure. The fraction of the heat energy that is converted into work is 

  1. $\dfrac 2 5$
  2. $\dfrac 2 7$
  3. $\dfrac 1 5$
  4. $\dfrac 5 7$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Supplied heat at constant pressure, 

$\Delta Q=nC _P \Delta T$
Change in internal energy,
$\Delta U=nC _V \Delta T$
ratio, $\dfrac{\Delta U}{\Delta Q}=\dfrac{nC _V \Delta T}{nC _P \Delta T}=\dfrac{C _V}{C _P}$. . . . . . . . .(1)
For diatomic ideal gas,
$C _P=\dfrac{7R}{2}\,  ,  C _V=\dfrac{5R}{2}$
From equation (1), we get
$\dfrac{\Delta U}{\Delta Q}=\dfrac{5R/2}{7R/2}=\dfrac{5}{7}$
$(5/7)^{th}$ part of heat supplied is used to increase internal energy.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

An ideal gas heat engine operates in a Carnot's cycle between $227^{\circ}C$ and $127^{\circ}C$. It absorbs $6\times 10^{4} J$ at high temperature. The amount of heat converted into work is _____.

  1. $4.8\times 10^{4}J$
  2. $3.5\times 10^{4}J$
  3. $1.6\times 10^{4}J$
  4. $1.2\times 10^{4}J$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Efficiency of Carnot engine = 1 - (T_low / T_high) = 1 - (400 / 500) = 0.2. Work done = Efficiency * Heat absorbed = 0.2 * 6 * 10^4 = 1.2 * 10^4 J.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

At a temperature T K,the pressure of 4.0 g argon in a bulb is p.The bulb is put in a bath having temperature higher by 50 K than the one.0.8 g of argon gas had to be removed to maintained ariginal pressure.The temperature T is equal to 

  1. 510 K

  2. 200 K

  3. 100 K

  4. 73 K
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using PV = nRT. Initially: pV = (4/M)RT. Finally: pV = (3.2/M)R(T+50). Equating: 4T = 3.2(T+50) => 4T = 3.2T + 160 => 0.8T = 160 => T = 200 K.

Multiple choice chemistry substances in the surroundings - their states and properties measurement of density properties of substances fundamental and derived units

Give reasons as to why equal masses of different substances have different volumes.

  1. because they have different shapes

  2. because they have different densities

  3. because they have the same densities

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The mass of the substance is dependent on the density and volume of the substance. The substance having the same volume might have different mass because they have different densities.


Option $B$ is correct. 

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If $T _i$ is the initial temperature and $T _f$ is the final temperature , which of the following is correct?

  1. $T _f>T _i$ for reversible process but $T _f=T _i$ for irreversible process
  2. $(T _f)rev=(T _f)irrev$
  3. $T _f=T _i$ for both reversible and irreversible process
  4. $(T _i)irrev>(T _f)rev$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\triangle Q=\triangle U+ \triangle W$


Isolated system- adiabatic $\Rightarrow \triangle Q=0$


$0=\triangle U+ \triangle W$

$\Rightarrow \triangle W=- \triangle U$

For expansion, $\triangle W$ is positive and $\triangle U$ is negative.
This means $T _f<T _i$

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics
Under which of the following conditions is the relation,
$\triangle H=\triangle U+P\triangle V$ valid for a closed system?

  1. Constant pressure

  2. Constant temperature

  3. Constant temperature and pressure

  4. Constant temperature, pressure and composition
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\Delta H=\Delta U+\Delta(PV)$

$\implies \Delta H=\Delta U+P\Delta V+V\Delta P$
In constant pressure/ Isobasic process
$\implies \Delta H=\Delta U+P\Delta V$

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

In which case mean free path is not affected? 

  1. ${ H } _{ 2 }$ gas at$ { 100 }^{ 0 }C$ and $1 \ atm $ is transferred into a vessel at $ { 50 }^{ 0 }C$ and $0.5 \ atm$
  2. ${ O } _{ 2 }$ gas at $200 K$ and $2 \ atm$ is transferred into a vessel at $400 K$ and $1\ atm $
  3. ${ O } _{ 2 }$ gas is replaced by ${ H } _{ 2 }$ gas keeping other variables constant

  4. Medium is made more viscous
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
${ H } _{ 2 }$ gas at ${ 100 }^{ 0 }C$ and $1atm$ is transferred into a vessel at ${ 50 }^{ 0 }C$ and $0.5atm$.
in this case $\dfrac { P }{ T } =$ constant.
In this case mean free path not affected.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Which of the following is path function?

  1. Work

  2. Specific volume

  3. Pressure

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

In thermodynamics, a state function or function of state is a function defined for a system relating several state variables or state quantities that depends only on the current equilibrium state of the system. State functions do not depend on the path by which the system arrived at its present state. A state function describes the equilibrium state of a system.

Hence, work is a path function and not state function.

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

An open vessel at $27^{\circ}C$ is heated until ($\tfrac 25$)th of the air in it has been expelled. Assuming that the volume of the vessel remains constant. Which of the following option is correct?

  1. Final temperature is 500 K

  2. Final volume is 2 times the initial volume

  3. Final pressure is 1 atm

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$T _{1}=27°C=27+273=300 K$


Let $n _{1}$ be n.

$n _{2}=n-\cfrac{2n}{5}=\cfrac{3n}{5}$

$T _{2}$=?

We know that, $n _{1}T _{1}=n _{2}T _{2}$

$\Longrightarrow n\times 300=\cfrac { 3n }{ 5 } \times { T } _{ 2 } \ \Longrightarrow { T } _{ 2 }=500K=500-273=227°C$

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

The state of gas can be described by quoting the relationship between_____________.

  1. pressure, volume, temperature

  2. temperature, amount, pressure

  3. amount, volume, temperature

  4. pressure, volume, temperature, amount
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pressure $(P)$, volume $(V)$, temperature $(T)$, amount $(n)$ etc. are the state variables or state functions.

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

A container of volume $1{m}^{3}$ is divided into two equal parts by a partition. One part has an ideal diatomic gas at $300K$ and the other part has vacuum. The whole system is isolated from the surrounding. When the partition is removed, the gas expands to occupy the whole volume. Its temperature will be:

  1. $300K$
  2. ${ 227.5 }^{ o }C$
  3. $455K$
  4. ${455}^{o}C$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is a free expansion of an ideal gas into a vacuum. Since the system is isolated (q=0) and expands into a vacuum (w=0), the internal energy remains constant (delta U = 0). For an ideal gas, internal energy depends only on temperature, so the temperature remains 300K.

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

The amount of heat necessary to raise the temperature of $0.2 \ mol\ of\ N _2$ at constant pressure from $37^oC$ to $ 337^oC$  will be

  1. $746\ J$
  2. $1746\ J$
  3. $2746\ cal$
  4. $3746\ J$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$N _2$ is a diatomic molecule thus its degree of freedom is 5. Its $C _p$ is given as $(1+\displaystyle\dfrac{f}{2})R=(1+\dfrac{5}{2})R=\dfrac{7}{2}R$
Thus, we get the heat required as $Q=nC _p\Delta T=0.2\times \displaystyle\dfrac{7}{2}\times 8.314\times 300=1746  J$

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

The specific heat of a gas at constant pressure as compared to that at constant volume is

  1. less

  2. equal

  3. more

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

When the gas is heated at constant pressure, some amount of heat is used up in increasing the volume of the gas. For a constant volume process no such heat is required. Thus $C _p>C _v$