Tag: basics of thermodynamics

Questions Related to basics of thermodynamics

Equal masses of hydrogen gas and oxygen gas are placed in a closed container at a pressure of $3.4 atm$. The contribution of hydrogen gas to the total pressure is:

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

  1. $1.7 atm$

  2. $0.2 atm$

  3. $3.2 atm$

  4. $3.02 atm$

Show answer
Correct Option: C
Explanation:

Let mass of hydrogen and oxygen be $100g$

$n 1=$ no of moles of hydrogen=$\cfrac {100}{2}=50$
$n _2=$ no of moles of oxygen=\cfrac {100}{32}=3.125$
Contribution of hydrogen to the total pressure means, mole fraction of hydrogen present in the mixture (partial pressure of $H_2$)
$X_4=\cfrac {n{H_2}}{n_{H_2}+n_{O_2}}=\cfrac {50}{50+3.125}=0.94$
Contribution of hydroegn to the total pressure= $0.94\times P=0.94 \times 3.4=3.2$ atm

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?

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

  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. $(T _i)irrev>(T _f)rev$

Show answer
Correct Option: D
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 $T _f<T _i$

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

  1. Constant pressure

  2. Constant temperature

  3. Constant temperature and pressure

  4. Constant temperature, pressure and composition

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Correct Option: A
Explanation:

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

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

In which case mean free path is not affected? 

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

  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

Show answer
Correct Option: A
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.

A well stoppered thermoflask contains some ice cubes. This is an example of:

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

  1. closed system

  2. open system

  3. isolated system

  4. non-thermodynamic system

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Correct Option: A

When a volatile liquid is introduced into an evacuated closed vessel at a particular temperature, both evaporation and condensation take place simultaneously. The system reaches equilibrium state when:

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

  1. the liquid is completely transformed into the corresponding vapour

  2. equal amounts of liquid and vapour are present in the system

  3. the rate of evaporation becomes equal to the rate of condensation

  4. liquid cannot be converted into vapour and vice versa.

Show answer
Correct Option: C
Explanation:
Solution:- (C) The rate of evaporation becomes equal to the rate of condensation
As we know that the equilibrium in a system is established when rate of forward reaction is equal to the rate of backward reaction.
Hence the rate of evaporation becomes equal to the rate of condensation.

Both q and w are ______ function and $q+w$ is a ______ function.

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

  1. state, state

  2. state, path

  3. path, state

  4. path, path

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Correct Option: C
Explanation:

Answer $C: $Path, state.

The change in energy of a system is equal to the difference between the heat added to the system and the work done by the system.
$\triangle E=Q-W$ ($W$ is $-ve$, if work done on system)
$Q$ and $W$ are path dependent, but $\triangle E$ depends only on the state of the system and not how the system got to that state.

A well stoppered thermos flask contains some ice cubes. This is an example of:

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

  1. closed system

  2. open system

  3. isolated system

  4. non-thermodynamic system

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Correct Option: C
Explanation:

An isolated system is a thermodynamic system that can not exchange either energy or matter outside the boundaries of the system.

Thus, a well stopped thermos flask containing ice an example for isolated system.

Which of the following is a path function?

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

  1. Internal Energy

  2. Enthalpy

  3. Work

  4. All of the above

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Correct Option: C
Explanation:
Path functions are properties or quantities whose values depend on the transition of a system from the initial state to the final state. The two most common path functions are heat and work

A physical quantity is said to be state function if its value depends only upon the state of the system and does not depend upon the path by which this state has been attained. E.g pressure, volume, temperature

Which of the following statement is false?

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

  1. Work is a state function.

  2. Temperature is a state function.

  3. Change of state is completely defined when initial and final states are specified.

  4. Work appears at the boundary of the system.

Show answer
Correct Option: A
Explanation:

Work is not a state function. It is path function. Its value depends on the path chosen to reach a particular state.