Tag: chemistry

Questions Related to chemistry

Select the state functions among the following:

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

  1. temperature

  2. entropy

  3. work

  4. enthalpy

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Correct Option: A,B,D
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.

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

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

  1. insulated

  2. isolated

  3. open

  4. closed

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Correct Option: D
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.

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:

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

  1. $3 : 2$

  2. $5 : 4$

  3. $2 : 1$

  4. $4 : 5$

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Correct Option: A
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 } $

Universe is :

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

  1. Closed system

  2. Open system

  3. Receiving constant supply of energy.

  4. Dissipating energy continuously.

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Correct Option: A
Explanation:

A closed system is one which can only exchange energy. The entire universe is an isolated system because it has no surrounding. Hence it is a closed system.

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

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

  1. $\triangle U=w\neq O,q=O$

  2. $\triangle U=w=q\neq O$

  3. $\triangle U=O,w=q\neq O$

  4. $w=O,\triangle U=q\neq O$

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Correct Option: A
Explanation:

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

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

For an isolated system, the entropy:

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

  1. Either increases or remains constant

  2. Either decreases or remains constant

  3. Can never decrease

  4. Can never increase

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Correct Option: A
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.

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

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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.