Tag: chemical thermodynamics

Questions Related to chemical thermodynamics

A closed system shows exchange of mass and not energy with surroundings.
chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. True

  2. False

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Correct Option: B
Explanation:

A closed system can exchange energy with surroundings. It cannot exchange mass with surroundings. For example, hot tea placed in a cup which is covered with saucer constitutes a closed system.

Which are extensive properties?

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

  1. $V$ and $E$

  2. $V$ and $T$

  3. $V$ and $Cp$

  4. $P$ and $T$

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Correct Option: A
Explanation:
An extensive property is a property that depends on the amount of matter in a sample. Mass and volume are examples of extensive properties.
Volume and energy both depends on amount of substance.

Hence, the correct option is $A$

Which thermodynamic parameter is not a state function ?

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

  1. q at constant pressure

  2. q at constant volume

  3. W at adiabatic

  4. W at isothermal

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Correct Option: D
Explanation:

$W$ and $q$ are not state functions

$H$ and $U$ are state functions
$\Delta H = \Delta U + \Delta PV$

At constant pressure, $\Delta H = \Delta U + P\Delta V$   $\Delta P = 0$   $\Delta H = q _p$

At constant volume, $\Delta H = \Delta U + V \Delta P$   $\Delta V = 0$   $\Delta U = q _v$

So, the first two options are state function.
$\Delta U = q - W$     $(\because q = 0)$    $[ \therefore$ Adialentic process$]$

$\Delta U = -W$  (state function)
Work done in isotheromal process is not a state
function
$W = -q  (\because \Delta T = 0, q \neq 0)$
$\therefore$ option D is correct.

Which of the following is path function? 


A. $W$
B. $Q$
C. $\Delta G$
D. $\Delta H$

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

  1. A and D

  2. A and B

  3. A, B and D

  4. A, C and D

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Correct Option: B

Identify the state functions from the following:

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

  1. heat

  2. work

  3. enthalpy

  4. none of the above

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Correct Option: C
Explanation:
Enthalpy is a state function. Its value depends on the current state of the system and is independent of the path followed to reach that state. Mass, temperature, pressure and volume are also state functions. Heat and work are path functions.

Among the following, the state functions are:

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

  1. Internal energy

  2. Irreversible expansion work

  3. Reversible expansion work

  4. Molar enthalpy

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Correct Option: A,D
Explanation:
State function is a quantity in thermodynamics, such as entropy or enthalpy, that has a unique value for each given state of a system. 
(or) 
A State Function is a thermodynamic quantity whose value depends only on the state at the moment, i. e., the temperature, pressure, volume, etc The value of a state function is independent of the history of the system's internal energy. Molar enthalpy and entropy are state quantities because they describe quantitatively an equilibrium state of a thermodynamic, irrespective of how the system arrived in that state.

Hence options A & D are correct.

A closed vessel contains equal number of nitrogen and oxygen molecules at a pressure of P mm. If nitrogen is removed from the system, then the pressure will be?

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

  1. P

  2. $2P$

  3. $P/2$

  4. $P^2$

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Correct Option: C
Explanation:

$\dfrac{p _1}{n _1}=\dfrac{p _2}{n _2}$ (As molecules of $N _2=$ molecules $O _2$)
($\therefore$ Moles $N _2=$moles $O _2$)
As $N _2$ molecules removed$=$ moles become half
$\dfrac{p _1}{1}=\dfrac{p _2}{1/2}$
$p=\dfrac{1}{2}p _1$
$\therefore$ Pressure reduced to half
$\therefore$ Answer is option C.

If a closed system has adiabatic boundaries, then atleast one boundary must be:

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

  1. permeable

  2. imaginary

  3. movable

  4. fixed

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Correct Option: C
Explanation:
Adiabatic boundaries mean there is no heat that is evolved or no heat exchange possible through it.

So, our system is closed that means matter cannot be exchanged but heat exchange can happen.

As here all the boundaries are adiabatic so to remain system closed at least one boundary should be movable to that heat exchange can take place.

Option C is correct.

Which of the following statement is correct?

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

  1. Heat is thermodynamic property of system.

  2. Work is thermodynamic property of system.

  3. Work done by a conservative force is path function.

  4. Heat involved in chemical reaction is path independent physical quantity.

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Correct Option: D
Explanation:
Heat and work are not thermodynamic properties and work done is independent of the object's path in a conservative force.

So, a,b,c are incorrect

A heat involved in the chemical reaction is path independent which is correct (from Hess's law)

Option D is correct.

The open system(s) is/are which

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

  1. can exchange matter with the surroundings

  2. can exchange energy with the surroundings

  3. can exchange both matter and energy with the surroundings

  4. cannot exchange either matter or energy with the surroundings

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Correct Option: A,B,C
Explanation:

Types of system : 
(i)Closed system : A system which can exchange only energy with surrounding. 
(ii)Open system : A system which can exchange both energy and matter with surrounding. 
(iii)Isolated system : A system which cannot exchange matter or energy with surrounding.