Thermodynamics Easy Questions and Answers | Page - 4

Thermodynamics

During an isothermal expansion, a confined ideal gas does –150 J of work against its surroundings. This implies that

1. 150 J heat has been removed from the gas
1. 300 J of heat has been added to the gas
1. no heat is transferred because the process is isothermal
1. 150 J of heat has been added to the gas
1. (a) or (d)

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If a process is expansion then work done is positive so answer will be (a).
But in question work done by gas is given –150J so that according to it answer will be (d).

Correct Option: E

If a process is expansion then work done is positive so answer will be (a).
But in question work done by gas is given –150J so that according to it answer will be (d).

If ∆U and ∆W represent the increase in internal energy and work done by the system respectively in a thermodynamical process, which of the following is true?

1. ∆U = -∆W in an adiabatic process
1. ∆U = ∆W in an isothermal process
1. ∆U = ∆W in an adiabatic process
1. ∆U = -∆W in an isothermal process

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By first law of thermodynamics,
∆Q = ∆U - ∆W
In adiabatic process, ∆Q = 0
∴ ∆U = -∆W
In isothermal process, ∆U = 0
∴ ∆Q = ∆W

Correct Option: A

By first law of thermodynamics,
∆Q = ∆U - ∆W
In adiabatic process, ∆Q = 0
∴ ∆U = -∆W
In isothermal process, ∆U = 0
∴ ∆Q = ∆W

In thermodynamic processes which of the following statements is not true?

1. In an isochoric process pressure remains constant
1. In an isothermal process the temperature remains constant
1. In an adiabatic process PV^γ = constant
1. In an adiabatic process the system is insulated from the surroundings

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In an isochoric process volume remains constant whereas pressure remains constant in isobaric process.

Correct Option: A

In an isochoric process volume remains constant whereas pressure remains constant in isobaric process.

If Q, E and W denote respectively the heat added, change in internal energy and the work done in a closed cyclic process, then :

1. W = 0
1. Q = W = 0
1. E = 0
1. Q = 0

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In a cyclic process, the initial state coincides with the final state. Hence, the change in internal energy is zero, as it depends only on the initial and final states. But Q & W are non-zero during a cycle process.

Correct Option: C

In a cyclic process, the initial state coincides with the final state. Hence, the change in internal energy is zero, as it depends only on the initial and final states. But Q & W are non-zero during a cycle process.

One mole of an ideal gas at an initial temperature of T K does 6R joules of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, the final temperature of gas will be

1. (T – 4) K
1. (T + 2.4) K
1. (T – 2.4) K
1. (T + 4) K

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T₁ = T , W = 6R joules , γ = 5
3

W = P₁V₁ - P₂V₂ = nRT₁ - nRT₂
γ - 1 γ - 1

= nR(T₁ - T₂)
γ - 1

n = 1 , T₁ = T ⇒ R(T - T₂) = 6R
(5 / 3) - 1

⇒ T₂ = ( T–4)K

Correct Option: A

T₁ = T , W = 6R joules , γ = 5
3

W = P₁V₁ - P₂V₂ = nRT₁ - nRT₂
γ - 1 γ - 1

= nR(T₁ - T₂)
γ - 1

n = 1 , T₁ = T ⇒ R(T - T₂) = 6R
(5 / 3) - 1

⇒ T₂ = ( T–4)K