Thermodynamics Test

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Thermodynamics Test - 11

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Question 1
1 / -0

The thermal motion means

A
motion due to heat engine

B
disorderly motion of the body as a whole

C
motion of the body that generates heat

D
random motion of molecules

Solution

Whenever a system absorbs heat from the surroundings or when we supply thermal energy to a system, the internal energy of the system increases. The heat absorbed increases the kinetic energy of the molecules causing them to move randomly.
Question 2
1 / -0

Internal energy per mole of gas depends on

A
viscosity

B
density

C
temperature

D
thermal conductivity

Solution

In a isochoric process , the volume of the system is kept constant. In the isochoric process, the heat energy supplied is absorbed as internal energy and does not cause a change in the work done by the system. The other terms used for isochoric process are iso - volumetric or isometric process.
Example: Gas heated in a tight container such as keeping a closed tin with air into fire.
Question 3
1 / -0

The laws of thermodynamics speak about

A
rates of chemical changes

B
feasibility and energy transformations of a

process

C
Both the rate and energy changes of a process

D
Energy changes in chemical reactions only

Solution

Thermodynamics laws are about energy transformation of a process and feasibility of a process
Question 4
1 / -0

The internal energy of an isolated system :

A
remains constant

B
keeps on changing

C
zero

D
may change depending on gas

Solution

From 1st law of thermodynamics,
$$\Delta Q = \Delta U + \Delta W$$
As the system is isolated from the surroundings, there is no heat transfer and the volume will remain constant.
Thus, work done is zero.
Using $$First \ Law \ of \ Thermodynamics$$, internal energy will be constant.
Question 5
1 / -0

The internal energy of a perfect gas depends on :

A
Pressure

B
Temperature

C
Volume

D
Specific heat

Solution

According to the assumptions of $$ Kinetic \ Theory \ of \ Gases$$, the molecules do not occupy any volume and attractive forces are absent between molecules of an ideal gas.
Thus, other parameters such as volume, pressure etc do not play a significant role in the internal energy of an ideal gas and is a function of temperature only.
For an ideal gas,
$$U=U(T)$$
where, U is the internal energy of the ideal gas.
T is the temperature of the ideal gas.
Question 6
1 / -0

The internal energy of an ideal gas depends upon

A
only its pressure

B
only its volume

C
only its temperature

D
its pressure and volume

Solution

$$\textbf{Explanation -}$$
Since, we know that - internal energy is sum of a gas of translation
kinetic energy and rotational kinetic energy and vibration energy.
But as a given - for ideal gas -
the gas possesses only translational kinetic energy

$$\bullet$$ Since we know that - energy of a gas per mole
per degree of freedom $$= \dfrac {1}{2} RT$$

So, $$U = \text {internal energy} = kE_{x} + kE_{y} + kE_{z}$$

$$U = \dfrac {1}{2} RT + \dfrac {1}{2}RT + \dfrac {1}{2}RT$$

$$U = \dfrac {3}{2} RT \rightarrow U\propto T$$

Hence option (C) is correct.
Question 7
1 / -0

The heat change in a chemical reaction at constant volume is given by:

A
$$\Delta H$$

B
$$\Delta E$$

C
$$\Delta T$$

D
$$\Delta V$$

Solution

First Law of Thermodynamics dictates that ΔQ=ΔE+ΔW
At constant V, ΔW=0
So, $$ \Delta Q = \Delta E$$
Question 8
1 / -0

Internal energy does not include

A
vibrational energy

B
rotational energy

C
energy arising by gravitational pull

D
nuclear energy

Solution

Energy arising by gravitational pull is not included in internal energy. Its external energy
Question 9
1 / -0

At the boiling point of water the saturated vapour pressure will be (in mm of Hg)

A
750

B
760

C
850

D
860

Solution

The boiling point of water is defined as the temperature at which the partial pressures of the water and steam are equal and thus equal to 760mm of Hg.
Question 10
1 / -0

Joule's experiment converts

A
work into heat

B
work into electricity

C
heat into work

D
electricity into work

Solution

Joule's experiment converts work into heat

Accurate investigation of the relationship between heat developed and mechanical work spent was taken up by the British Scientist James Prescott Joule. The main aim of his investigations was to determine exactly the ratio between the work done and the quantity of heat produced.

Joule used different arrangements for doing the work, W in different ways and measured the corresponding amount of heat, H produced in each case. In all the cases he found that the expenditure of the same amount of work always produced the same amount of heat. Every time he found that 4186 joule of work was spent to produce the same amount of heat which could raise the temperature of one kg of water through 10C. He established the relation, W/H to be a constant quantity. The constant relation W/H was represented symbolically by the letter ‘J’. J is known as Joule's mechanical equivalent of heat. ‘Symbolically, we can write :

W/H = J or W = JH

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Thermodynamics Test - 11

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Question 1

motion due to heat engine

disorderly motion of the body as a whole

motion of the body that generates heat

random motion of molecules

Solution

Question 2

viscosity

density

temperature

thermal conductivity

Solution

Question 3

rates of chemical changes

feasibility and energy transformations of aprocess

Both the rate and energy changes of a process

Energy changes in chemical reactions only

Solution

Question 4

remains constant

keeps on changing

zero

may change depending on gas

Solution

Question 5

Pressure

Temperature

Volume

Specific heat

Solution

Question 6

only its pressure

only its volume

only its temperature

its pressure and volume

Solution

Question 7

$$\Delta H$$

$$\Delta E$$

$$\Delta T$$

$$\Delta V$$

Solution

Question 8

vibrational energy

rotational energy

energy arising by gravitational pull

nuclear energy

Solution

Question 9

750

760

850

860

Solution

Question 10

work into heat

work into electricity

heat into work

electricity into work

Solution

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feasibility and energy transformations of a

process