Thermodynamics Test

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Thermodynamics Test - 5

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Weekly Quiz Competition

Question 1
1 / -0

A system is changed from an initial state to a final state by a process such that ∆H = q. If the change from the initial state to the final state were measured by a different path, what would be observed?

A
∆H is different for different paths, but q remains the same.

B
∆H is the same, but q is different for different paths.

C
Both ∆H and q are the same.

D
Both ∆H and q are different for different paths.

Solution

∆H is the same because it is a state function and q, being a path function, will be different for different paths.
Question 2
1 / -0

A Path function is

A
a property of a system that depends only on the current state of the system, not on the path the system took to reach that state

B
a property of a system that depends on the path taken between the initial and final states

C
the sum of kinetic and potential energies contained in a substance

D
the temperature change recorded when heat is either supplied to the system or removed from the system

Solution

A property is considered a path function if its value depends on the path taken between the initial and final states, e.g. work done and heat absorbed.
The property whose value does not depend on the path taken but only on the initial and final states of the system is said to be a state function.
Question 3
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Consider the following thermodynamic properties:

(i) Work done on a system
(ii) Heat absorbed
(iii) Entropy
(iv) Enthalpy

Which of the above is/are state functions?

A
(i) and (ii)

B
Only (iii)

C
(ii) and (iii)

D
(iii) and (iv)

Solution

Work done and heat absorbed by a system depend on the route taken between the initial and final states. Entropy is a function that measures the disorder within a system. Enthalpy depends on the heat energy absorbed by a system. Both entropy and enthalpy have values that do not depend on the path the system has taken. Therefore, they are both state functions.
Question 4
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The work done can be calculated from pV–plot by using the area under the curve within specific limits when an ideal gas is compressed (a) reversibly or (b) irreversibly from volume V_i to V_f. Choose the correct option.

A
w (reversible) = w (irreversible)

B
w (reversible) < w (irreversible)

C
w (reversible) > w (irreversible)

D
w (reversible) = w (irreversible) + p_ex. ∆V

Solution

This is because work done is always more in a reversible process.
Question 5
1 / -0

A system does 100 J work on its surroundings by absorbing 150 J of heat. Calculate the change in internal energy.

A
100 J

B
50 J

C
25 J

D
150 J

Solution

Heat absorbed by the system, q = +150 J
Work done by the system, w = -100 J
According to the first law of thermodynamics,
∆U = q + w = 150 – 100 = 50 J
Question 6
1 / -0

A 1 kg block of ice at 0ºC is placed into a perfectly insulated sealed container that has 2 kg of water, also at 0ºC. Water and ice completely fill the container, but the container is flexible. After some time,

A
water will freeze so that the mass of ice will increase

B
ice will melt so that the mass of ice will decrease

C
both the amount of water and the amount of ice will remain constant

D
both the amount of water and the amount of ice will decrease

Solution

Ice will melt so that the mass of ice will decrease.
In accordance with second law of thermodynamics, if an irreversible process occurs in a closed system, the entropy of that system always increases; it never decreases. Entropy measures the state of disorder. As ice is more ordered than water, so ice will melt so that the mass of ice will decrease.
Question 7
1 / -0

The volume of a gas is reduced to half its original volume. The specific heat of the gas will

A
be doubled

B
increase four times

C
remain constant

D
be reduced to half

Solution

The specific heat will remain constant. It is an intensive property and depends upon the nature of the gas.

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Thermodynamics Test - 5

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Thermodynamics Test - 5

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Question 1

∆H is different for different paths, but q remains the same.

∆H is the same, but q is different for different paths.

Both ∆H and q are the same.

Both ∆H and q are different for different paths.

Solution

Question 2

a property of a system that depends only on the current state of the system, not on the path the system took to reach that state

a property of a system that depends on the path taken between the initial and final states

the sum of kinetic and potential energies contained in a substance

the temperature change recorded when heat is either supplied to the system or removed from the system

Solution

Question 3

(i) and (ii)

Only (iii)

(ii) and (iii)

(iii) and (iv)

Solution

Question 4

w (reversible) = w (irreversible)

w (reversible) < w (irreversible)

w (reversible) > w (irreversible)

w (reversible) = w (irreversible) + pex. ∆V

Solution

Question 5

100 J

50 J

25 J

150 J

Solution

Question 6

water will freeze so that the mass of ice will increase

ice will melt so that the mass of ice will decrease

both the amount of water and the amount of ice will remain constant

both the amount of water and the amount of ice will decrease

Solution

Question 7

be doubled

increase four times

remain constant

be reduced to half

Solution

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w (reversible) = w (irreversible) + p_ex. ∆V