Tag: introduction to thermodynamics

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

Which of the following is path function? 


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

  1. A and D

  2. A and B

  3. A, B and D

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

Path functions depend on the process taken to reach a state, not just the state itself. Work (W) and Heat (Q) are path functions, whereas internal energy, enthalpy (H), and Gibbs free energy (G) are state functions.

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

Identify the state functions from the following:

  1. heat

  2. work

  3. enthalpy

  4. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Among the following, the state functions are:

  1. Internal energy

  2. Irreversible expansion work

  3. Reversible expansion work

  4. Molar enthalpy
Reveal answer Fill a bubble to check yourself
A,D Correct answer
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.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

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?

  1. P
  2. $2P$
  3. $P/2$
  4. $P^2$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. permeable

  2. imaginary

  3. movable

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

Which of the following statement is correct?

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

The open system(s) is/are which

  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
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
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.

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

The enthalpy change for a reaction does not depend upon the:

  1. physical states of reactants and products

  2. use of different reactants for the same product

  3. nature of intermediate reaction steps

  4. difference in initial or final temperature of involved substances
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\triangle H$ depends on :

  • Physical states of reactant and product.
  • Use of different reactants for the same product.
  • Difference in initial or final temperature of involved substances.
It is independent of nature of intermediate reaction steps because it is a path independent & is a state function.

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics
The change in enthalpy, $\Delta H$ accompanying a process depends on the path followed.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The change in enthalpy, $\Delta H$ accompanying a process does not depends on the path followed.
This is because the enthalpy of a reaction is a state function and its value depends on the inital and final states only.

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics
  Column I   Column II
a. Enthalpy p. Intrinsic property
b. Temperature q. Path function
c. Free energy r. Function $U, P, V$
d. Work s. State function
  1. $(a - r,s), (b - p,s), (c - r,s), (d - q)$
  2. $(a - r), (b - s), (c - r,s), (d - q, r)$
  3. $(a - r,s), (b - r), (c - p,s), (d - q)$
  4. $(a - q), (b - p,s), (c - s), (d - q, s)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$(a\rightarrow r,s)$ Enthalpy is a state function and is a function of internal energy and pressure and volume.
$(b\rightarrow p,s)$ Temperature is independent of the bulk matter of the system and hence it is an intrinsic property but it is a state variable.
$(c\rightarrow r,s)$ Free energy is a state function as it depends on the state of the system as well as it depends on $H, T$ and $S$. It is also a function of $U, P$ and $V$.
$(d\rightarrow q)$ Work is a path function as the amount of work done depends upon path undertaken.