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

Select the state functions among the following:

  1. temperature

  2. entropy

  3. work

  4. enthalpy
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

State function is defined as a system that depends upon the initial and final positions,

so temperature , entropy and enthalpy depends upon the initial and final state, so they are state function but work depends upon the area of PV curve.

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

A system where there is exchange of energy but not of mass is called _________ system.

  1. insulated

  2. isolated

  3. open

  4. closed
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In thermodynamics, a closed system can exchange energy (as heat or work) but not matter, with its surroundings. An isolated system cannot exchange any heat, work, or matter with the surroundings, while an open system can exchange energy and matter.

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

Temperatures of two hot bodies $B _{1}$ and $B _{2}$ are $100^{\circ}C$ and $80^{\circ}C$ respectively. The temperature of surrounding is $40^{\circ}C$. At $t = 0$, the ratio of rates of cooling of the two bodies (liquid) $R _{1} : R _{2}$ will be:

  1. $3 : 2$
  2. $5 : 4$
  3. $2 : 1$
  4. $4 : 5$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rate of cooling=$\cfrac { dQ }{ dt } \propto \quad \Delta T$ 

$\therefore \cfrac { { R } _{ 1 } }{ { R } _{ 2 } } =\cfrac { { \Delta T } _{ 1 } }{ { \Delta T } _{ 2 } } =\cfrac { 100-40 }{ 80-40 } =\cfrac { 60 }{ 40 } =\cfrac { 3 }{ 2 } $

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

In a closed insulator container, a liquid is stirred with a paddle to increase the temperature. Which of the following is true?

  1. $\triangle U=w\neq O,q=O$
  2. $\triangle U=w=q\neq O$
  3. $\triangle U=O,w=q\neq O$
  4. $w=O,\triangle U=q\neq O$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A closed insulated container, a liquid is stirred with a paddle to increase the temperature, therefore it behave as adiabatic system, $q=0$

$\Delta U=q+w$
$\implies \Delta U=w\neq 0$

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

For an isolated system, the entropy:

  1. Either increases or remains constant

  2. Either decreases or remains constant

  3. Can never decrease

  4. Can never increase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy.

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.