Top

# Thermodynamics

1.

Mass and energy are conserved quantities, but entropy is generally not conserved.

This is a basic fact about entropy.

Enter details here

2.

A hot metal piece is cooled rapidly to 25°C, removing 1000 kJ from the metal. Calculate the change of entropy if energy is absorbed by vaporizing liquid nitrogen at 101.3 kPa pressure.

Nitrogen boiling at 101.3 kPa; m = 1Q2 /h(fg) = 1000/198.842 = 5.029 kg
∆S(N2) = ms(fg) = 5.029(2.5708) = 12.929 kJ/K.

Enter details here

3.

Which of the following is a type of energy?

These are two types in which the sources of energy can be divided into.

Enter details here

4.

A piston cylinder contains 0.5 kg of air at 500 kPa and 500 K. The air expands in a process so pressure is linearly decreasing with volume to a final state of 100 kPa and 300 K. Find the work in the process.

Work = ⌠ PdV = (1/2)(P1 + P2)(V2 – V1)
V1 = mR T1/ P1 = 0.5 × 0.287 × (500/500) = 0.1435 m^3
V2 = mR T2/ P2 = 0.5 × 0.287 × (300/100) = 0.4305 m^3
W = (1/2)(500 + 100)(0.4305 – 0.1435) = 86.1 kJ.

Enter details here

5.

At equilibrium, the isolated system exists at the peak of the entropy-hill and

At equilibrium, the entropy becomes maximum and hence change in entropy is zero.

Enter details here

6.

If the path A causes more entropy generation than path B, then

The amount of entropy generation quantifies the intrinsic irreversibility of the process.

Enter details here

7.

A piston-cylinder device initially contains air at 150 kPa and 27°C. At this state, the volume is 400 litre. The mass of the piston is such that a 350 kPa pressure is required to move it. The air is now heated until its volume has doubled. Determine the total heat transferred to the air.

Qin – Wout = ΔU = m(u3 –u1)
m = P1V1/RT1 = 0.697 kg
u1 = u@ 300 K = 214.36 kJ/kg
u3 = u@ 1400 K = 1113.43 kJ/kg
Therefore Qin = 767 kJ.

Enter details here

8.

The proof that work done in all reversible processes is same can be done by violating Kelvin-Planck statement.

During the proof, we end up violating the Kelvin-Planck statement.

Enter details here

9.

The available energy is known as ____ and the unavailable energy is known as ____

Rant was the one who coined these terms.

Enter details here

10.

Which of the following is the largest unit of energy?

No answer description available for this question.

Enter details here