Tag: introduction to thermodynamics

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Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics 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:

  1. $1.7 atm$
  2. $0.2 atm$
  3. $3.2 atm$
  4. $3.02 atm$
Reveal answer Fill a bubble to check yourself
C Correct answer
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

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

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

  1. closed system

  2. open system

  3. isolated system

  4. non-thermodynamic system
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A thermoflask is designed to prevent the exchange of heat (energy) and matter with the surroundings, making it an isolated system. However, in many textbook contexts, if it is 'well-stoppered' but not perfectly insulated, it is often treated as a closed system regarding matter.

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

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:

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

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

  1. state, state

  2. state, path

  3. path, state

  4. path, path
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. closed system

  2. open system

  3. isolated system

  4. non-thermodynamic system
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Which of the following is a path function?

  1. Internal Energy

  2. Enthalpy

  3. Work

  4. All of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
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

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

Which of the following statement is false?

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

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