Tag: chemical thermodynamics

Questions Related to chemical thermodynamics

Choose the correct answer. 

A thermodynamic state function is a quantity : 

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

  1. used to determine heat chages

  2. whose value is independent of path

  3. used to determine pressure volume work

  4. whose value depends on temperature only

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Correct Option: B
Explanation:

A thermodynamic state function is a quantity whose value is independent of path. Thus, enthalpy is a state function.
Its value depends on iniital and final states and is independatn of path followed.

Among the following, the state function are

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

  1. internal energy

  2. molar enthalpy

  3. reversible expansion work

  4. irreversible expansion work

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Correct Option: A,B
Explanation:

State functions are path Independent

For example: $E$ (Internal energy), Molar enthalpy, entropy etc.

Why are state functions important in chemistry?

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

  1. They appear a lot in thermochemistry and thermodynamics

  2. Many equations include properties that are state functions

  3. We only need to know the final and initial states

  4. They simplify our calculations

  5. All answers are correct

Show answer
Correct Option: C
Explanation:
State functions help us simplify our calculations and see the change in value between the final and starting position, also known as a state change. Mass, pressure, density, energy, temperature, volume, enthalpy, entropy, Gibbs free energy and chemical composition are all examples of state functions in thermochemistry
In simple words, the state functions are important in chemistry as we only need to know the final and initial states.

Hence, the correct option is $C$

Which statement is correct?

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

  1. The final destination is not important with state functions

  2. The change in altitude was the same for the train and the hikers, therefore the change in altitude is a state function

  3. The starting point is not important with state functions

  4. The hikers put more effort into climbing therefore the change in altitude is not a state function

  5. None of these
Show answer
Correct Option: B
Explanation:

The statement B is correct.
The change in altitude was the same for the train and the hikers, therefore the change in altitude is a state function. The value of state function depend only on initial and final value and is independent of the path followed.

Which statement BEST describes why work is a path function

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

  1. You finish at a different place

  2. You start at a different place

  3. The amount of work varies depending on which path you take to get to the destination

  4. The amount of work is the same whichever path you take to get to the destination

  5. Work is not a path function, it is a state function

Show answer
Correct Option: C
Explanation:

The statement (C) BEST describes why work is a path function.
The amount of work varies depending on which path you take to get to the destination.
State function is independent of the pah followed whereas path function is dependent on path followed.

Consider the following reaction, taking place in a container fitted with a movable piston.
$2SO _{2}(g) + O _{2}(g) \rightarrow 2SO _{3}(g)$
Suppose we place two moles each of $SO _{2}$ and $O _{2}$ in the reaction vessel at $25^{\circ}C$, and adjust the volume to give a total pressure of $1.0\ atm$. The reaction is ignited by a spark, and goes to completion. The temperature is returned to $25^{\circ}$.
Which of the following best describes this system after reaction is complete?

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

  1. $SO _{2}$ is limiting. The volume of the system remains the same.

  2. Neither reactant is limiting. The volume of the system decreases.

  3. $SO _{2}$ is limiting. The volume of the system decreases.

  4. $O _{2}$ is limiting. The volume of the system remains the same.

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Correct Option: A

Which describes an endothermic reaction?

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

  1. Positive $\displaystyle \Delta H$

  2. Negative $\displaystyle \Delta H$

  3. Positive $\displaystyle \Delta G$

  4. Negative $\displaystyle \Delta G$

  5. Positive $\displaystyle \Delta S$

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Correct Option: A
Explanation:

The term endothermic process describes a process or reaction in which the system absorbs energy from its surroundings so enthalpy change should be positive

Which of the following statements are correct?

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

  1. $\Delta H$ is a state function

  2. Value of $\Delta H $ is independent of path taken

  3. $\Delta H$ can be determined under standard condition

  4. All of the above

Show answer
Correct Option: D
Explanation:

Change in enthalpy $\triangle H$ is a state function as its value doesn't depend on the path taken i.e. they give a unique value for each given state of a system. Since it gives value independent of path taken, its value at standard condition can be determined(25℃ and 1atm)
Hence all statements are correct.

Which of the following statements are not true?

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

  1. Heat is a macroscopic physical property

  2. Heat is an intrinsic property of a body

  3. Heat is stored in a body as internal energy

  4. Heat is path independent

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Correct Option: B,D
Explanation:

An intrinsic property is a property of a system or of a material itself or within. It is independent of how much of the material is present and is independent of the form of the material. Heat flow is a results of a temperature difference between two bodies hence, it is not an intrinsic property of substance.

Two important examples of a path function are heat and work. These two functions are dependent on how the thermodynamic system changes from the initial state to final state.

Which of the following functions are path independent?

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

  1. Work

  2. Heat

  3. Gravitational potential energy

  4. Internal energy

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Correct Option: C,D
Explanation:

In thermodynamics, a state function or function of state is a function defined for a system relating several state variables or state quantities that depends only on the current equilibrium state of the system. State functions do not depend on the path by which the system arrived at its present state. A state function describes the equilibrium state of a system.

For example, internal energy, enthalpy, Gravitational potential energy and entropy are state quantities because they describe quantitatively an equilibrium state of a thermodynamic system, irrespective of how the system arrived in that state.