Thermodynamics Test

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Thermodynamics Test - 14

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Weekly Quiz Competition

Question 1
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Which of the following process is non-spontaneous?

A
Heat flow from hot end to cool end.

B
Water flow from higher level to lower level.

C
Gas flow from lower pressure region to higher pressure region.

D
Gas flow from higher pressure region to lower pressure region.

Solution

Gas flowing from higher pressure region to lower pressure region is a natural process. Similarly, option A and B are natural. Natural processes are spontaneous. Therefore, flow of gas from lower pressure to higher pressure region is non-spontaneous.
Question 2
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Energy hidden in a definite quantity of substance is:

A
Enthalpy

B
Internal energy

C
Free energy

D
Entropy

Solution

Internal energy is the hidden energy in a definite quantity of substance
Question 3
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Which of the following relations is not correct?

A
$$G=H-TS$$

B
$$\Delta G_{system} = \Delta H _{system} T \Delta S_{system}$$

C
$$T \Delta S_{system} = \Delta H_{system} -\Delta G_{system}$$

D
$$\Delta H_{system} =\Delta G _{system} + T\Delta S_{system}$$

Solution

$$G $$=$$ H - TS$$

$$\Rightarrow \Delta G_{system}=\Delta H_{system}-T\Delta S_{system}$$

$$\Rightarrow T\Delta S_{system}=\Delta H_{system}-\Delta G_{system}$$

$$\Rightarrow \Delta H_{system}=\Delta G_{system}+T\Delta S_{system}$$

Thus, option $$B$$ is not correct relation.

Hence, the correct option is $$B$$
Question 4
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Hess's law of constant heat summation is based on

A
E = mc$$^{2}$$

B
conservation of mass

C
first law of thermodynamics

D
E = h$$\nu $$
Solution
Hint: Hess's law of constant heat summation states that " Regardless of multiple stages, total enthalpy changes is the sum of all the changes."

Correct answer: Option $$C$$

$$\bf{Explanation \ for \ Correct \ Option}:$$
Mathematically Hess law can be represented as;
$$ \Delta H_{net} = \sum \Delta H_r$$
Where, $$ \Delta H_{net}$$ = Net enthalpy change
$$\Delta H_r$$ =Sum of enthalpy change of reactions
So, Enthalpy change is a state function as it depends on the final and initial stage and not the path followed by the system.
So, It resembles internal energy as internal energy is also a state function.
The first law of thermodynamics states that " Some part of internal energy of the system is used to heat the system while another part is used for work done."
So, Hess's law of constant heat summation is based on the first law of thermodynamics as both suggest the conversation of energy.

$$\bf{Explanation \ for \ Incorrect \ Options}$$
The statement $$E = mc^2$$ suggests the relationship between mass and energy and Hess's law deals with energy only.
In Hess law conservation of energy takes place and not conservation of mass.
$$E = h \mu$$ suggest that energy is quantized so it does not represent Hess law.
Question 5
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All natural processes are:

A
Spontaneous

B
Non- spontaneous

C
Exothermic

D
Endothermic

Solution

A spontaneous process is one that occurs on its own, without any energy used from the outside. For example, a ball will roll down an incline; water will flow downhill; ice will melt into water; radioisotopes will decay; and iron will rust.
So all natural process are spontaneous.
Henceoption A is correct.
Question 6
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The heat change associated with reactions at constant volume is due to the difference in which property of the reactants and the products ?

A
internal energy

B
enthalpy

C
heat capacity

D
free energy

Solution

First Law of Thermodynamics dictates that $$ \Delta Q = \Delta U + \Delta W$$
At constant V, $$ \Delta W = 0$$
So, $$ \Delta Q = \Delta U$$
So at constant volume, heat change takes place due to change in internal energy of the system
Question 7
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Hess’s law deals with:

A
heat changes in a chemical reaction.

B
rate of reaction

C
equilibrium constant

D
influence of pressure on volume of a gas

Solution

Hess law deals with the heat changes in a chemical reaction
Question 8
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Which type of molecular motion does contribute towards internal energy for an ideal mono-atomic gas?

A
Translational

B
Rotational

C
Vibrational

D
All of the above

Solution

$$U =\dfrac{f}{2}N \ k \ T$$ where f = number of degrees of freedom
In an ideal mono-atomic gas, the internal energy is contributed only due to the translational kinetic energy.
For example if we take He or Ne, the atoms are not bound to each other and hence they do not vibrate. Rotational energy is neglected since their atomic moment of inertia is minimal and higher energy excitation electronically also is not possible (except at very high temperatures).
Thus, the internal energy changes in an ideal mono atomic gas are purely translational and there are 3 degrees of freedom. In other words translation can take place in 3D space i.e. x, y and z directions.
If there are N atoms in the gas, the total energy U is given by
$$U =\dfrac{3}{2}N \ k \ T$$
Question 9
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The total heat content of a system is

A
Entropy

B
Free energy

C
Enthalpy

D
Kinetic energy

Solution

Enthalpy (H) is the sum of the internal energy (U) and the product of pressure and volume (PV) given by the equation: H = U + PV
Question 10
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$$\Delta H_{f}=$$ -98.2 K.Cal/mole
$$S_{Na} =$$ 36 K.Cal/mole
$$I_{Na} =$$ 118.5 K.Cal/mole
$$\dfrac{1}{2}D_{Cl_{2}}=$$ 29 K.Cal/mole
$$U_{NaCl}=$$ -184.2 K.Cal/mole
From the data given below for $$NaCl$$, the electron affinity of chlorine $$[-E_{a}]$$ is:

A
-97.5 K.cal/ mole

B
-108 K.cal/mole

C
-75 K.cal/mole

D
-128 K.cal/mole

Solution

From Born-Haber Cycle,
We have,
$$\Delta H_f = S_{Na} + I_{Na} + \frac {1}{2} D_{Cl_2} + E_a + U_{NaCl}$$
$$-98.2 = 36 + 118.5 + 29 + (-184.2) + E_a$$
$$E_a = -97.5 K. Cal/mole$$

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Thermodynamics Test - 14

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Thermodynamics Test - 14

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Question 1

Heat flow from hot end to cool end.

Water flow from higher level to lower level.

Gas flow from lower pressure region to higher pressure region.

Gas flow from higher pressure region to lower pressure region.

Solution

Question 2

Enthalpy

Internal energy

Free energy

Entropy

Solution

Question 3

$$G=H-TS$$

$$\Delta G_{system} = \Delta H _{system} T \Delta S_{system}$$

$$T \Delta S_{system} = \Delta H_{system} -\Delta G_{system}$$

$$\Delta H_{system} =\Delta G _{system} + T\Delta S_{system}$$

Solution

Question 4

E = mc$$^{2}$$

conservation of mass

first law of thermodynamics

E = h$$\nu $$

Solution

Question 5

Spontaneous

Non- spontaneous

Exothermic

Endothermic

Solution

Question 6

internal energy

enthalpy

heat capacity

free energy

Solution

Question 7

heat changes in a chemical reaction.

rate of reaction

equilibrium constant

influence of pressure on volume of a gas

Solution

Question 8

Translational

Rotational

Vibrational

All of the above

Solution

Question 9

Entropy

Free energy

Enthalpy

Kinetic energy

Solution

Question 10

-97.5 K.cal/ mole

-108 K.cal/mole

-75 K.cal/mole

-128 K.cal/mole

Solution

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