Tag: chemistry

Questions Related to chemistry

The work done in an open vessel at $300$K, when $112g$ iron reacts with dilute $HCl$ to give $FeCl _2$, is nearly:

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

  1. $1.1$ kcal

  2. $0.6$ kcal

  3. $0.3$ kcal

  4. $0.2$ kcal

Show answer
Correct Option: A
Explanation:
The reaction involved is:
$Fe+2HCl \rightarrow FeCl _2+H _2$
Atomic mass of $Fe=56 g/mol $
Thus, 56 g of Iron reacts with 2 moles of HCl to give one mole of Hydrogen gas.
Initial volume of $H _2$ gas = $V _1 = 0$
Final volume of $H _2$ gas=$ V _2$
Using ideal gas law:$PV = n R T$
where n=mass/molar mass, R=8314 J/K/mol and given that T=300 K
$PV _2 = (112/56) \times 8.314 \times 300 = 4988.4J$
Work done $= -P \Delta V=-P(V _2 - V _1) =-P V _2 = -4988.4J$
negative work done is work of expansion.
since 4184 J=1 kcal
thus $4988.4 J=1.19 kcal$ of work is done by the system.

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?

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

  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

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Correct Option: A
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, $n _{1}T _{1}=n _{2}T _{2}$

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

An open vessel containing air is heated from 300 K to 400 K. The fraction of air originally present which goes out of it is:

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

  1. 3/4

  2. 1/4

  3. 2/3

  4. 1/8

Show answer
Correct Option: B
Explanation:
 
According to ideal gas equation
$PV = nRT$
$\Rightarrow \; n \propto \cfrac{1}{T}$
$\Rightarrow \; \cfrac{{n} _{1}}{{n} _{2}} = \cfrac{{T} _{2}}{{T} _{1}}$
Given that:-
${n} _{1} = 1$ 
${T} _{1} = 300K$, 
${T} _{2} = 400K$ 
${n} _{2} = ?$
$\therefore \; \cfrac{1}{{n} _{2}} = \cfrac{400}{300}$
${n} _{2} = \cfrac{3}{4}$
The fraction of air present in the vessel after heating ${n} _{2} = \cfrac{3}{4}$
The fraction of air which goes out of the vessel $= 1 - \cfrac{3}{4} = \cfrac{1}{4}$

System in which there is no exchange of matter, work or energy from surroundings is:

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

  1. closed

  2. adiabatic

  3. isolated

  4. isothermal

Show answer
Correct Option: C
Explanation:

Closed System - The system in which only energy can be exchanged with the surrounding.


Adiabatic - The process in which heat is not exchanged by the system with the surroundings, i.e., $Q=0$.


Isolated - The system in which neither energy nor matter can be exchanged with the surroundings.  

Isothermal - The temperature remains constant, i.e., $\Delta T=0$.


Hence, the correct answer is option $\text{C}$.

In a closed system : $A\left( s \right) \rightleftharpoons 2B\left( g \right) +3C\left( g \right) $ if the partial pressure C is of doubled then partial pressure B wil be:

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

  1. Twice the original pressure

  2. Half of its original pressure

  3. $\dfrac { 1 }{ 2\sqrt { 2 } } $ times, the original pressure

  4. $2\sqrt { 2 } $ times its original pressure

Show answer
Correct Option: C
Explanation:
Solution:- (C) $\cfrac{1}{2 \sqrt{2}}$ times, the original pressure
${A} _{\left( s \right)} \rightleftharpoons 2 {B} _{\left( g \right)} + 3 {C} _{\left( g \right)}$
${K} _{P} = {\left( {P} _{B} \right)}^{2} {\left( {P} _{C} \right)}^{3} ..... \left( 1 \right)$
If we double the partial pressure of $C$, i.e., ${P} _{C}' = 2 {P} _{C}$
$\therefore {K} _{P}' = {\left( {P} _{B}' \right)}^{2} {\left( {P} _{C}' \right)}^{3}$
$\Rightarrow {K} _{P}' = {\left( {P} _{B}' \right)}^{2} {\left( 2 {P} _{C} \right)}^{3}$
$\Rightarrow {K} _{P}' = 8 {\left( {P} _{B}' \right)}^{2} {\left( {P} _{C} \right)}^{3}$
Since ${K} _{P}$ is constant,
$\therefore {K} _{P} = {K} _{P}'$
$\Rightarrow {\left( {P} _{B} \right)}^{2} {\left( {P} _{C} \right)}^{3} = 8 {\left( {P} _{B}' \right)}^{2} {\left( {P} _{C} \right)}^{3}$
$\Rightarrow {P} _{B}' = \sqrt{\cfrac{{P} _{B}}{8}}$
$\Rightarrow {P} _{B}' = \cfrac{{P} _{B}}{2 \sqrt{2}}$
Hence the partial pressure of $B$ will be $\cfrac{1}{2 \sqrt{2}}$ times of its original pressure.

Which of the following statement is correct?

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

  1. The presence of reaction species in a covered beaker is an example of open system.

  2. There is an exchange of energy as well as matter between the system and the surroundings in a closed system.

  3. The presence of reactants in a closed vessel made up of copper is an example of a closed system.

  4. The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system.

Show answer
Correct Option: C
Explanation:

In a closed system (For example, the presence of reactants in a closed vessel made of conducting material e.g copper) there is no exchange of matter, but exchange of energy is possible between system and the surroundings.

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

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

  1. pressure, volume, temperature

  2. temperature, amount, pressure

  3. amount, volume, temperature

  4. pressure, volume, temperature, amount

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Correct Option: D
Explanation:

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

Select incorrect statement(s):

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

  1. A closed system with all adiabatic boundaries must be an isolated system

  2. Total heat exchange in a cyclic process may be zero

  3. Entropy of a closed system is maximum at equilibrium

  4. Molar gibb's Energy is an extensive property

Show answer
Correct Option: A
Explanation:
Since heat is energy, only two systems can stop it from crossing the boundary closed and isolated system. So yes, adiabatic process can happen in an isolated system. But all adiabatic process need not happen in an isolated system, it can happen in a closed system also.

Two closed vessel $A$ and $B$ of equal volume of $8.21L$ are connected by a narrow tube of negligible volume with open valve. The left hand side container id found to contain $3\ mole \, CO _2$ and $2\ mole$ of $He$ at $400K$. What is the partial pressure of $He$ in vessel $B$ at $500K$?

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

  1. 2.4 atm

  2. 8 atm

  3. 12 atm

  4. None of these

Show answer
Correct Option: B
Explanation:

partial pressure of $He$ in vessel $B$, 

$PV = nRT$
$P _{He} = \dfrac{nRT}{V} = \dfrac{2\times 8.314\times 400}{8.21} =8atm$

Ammonium carbamate dissociates as ${ NH } _{ 2 }COON{ H } _{ 4\left( s \right)  }\leftrightharpoons 2N{ H } _{ 3\left( g \right)  }+{ CO } _{ 2\left( g \right)  }$. In a closed vessel containing ammonium carbamate in equilibrium, ammonia is added such that the partial pressure of ${ NH } _{ 3 }$ now equals to the original total pressure. The ratio of total pressure now to the original pressure is :

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

  1. $\frac { 27 }{ 31 } $

  2. $\frac { 31 }{ 27 } $

  3. $\frac { 4 }{ 9 } $

  4. $\frac { 5 }{ 9 } $

Show answer
Correct Option: B