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Perpetual motion machine of the second kind

Perpetual motion machine of the second kind  Perpetual motion machine of the second kind is a machine which produces work from a single heat source. In this kind of perpetual …

Example : Entropy of gas spring system

In the spring-gas system before An ideal gas is contained in a cylinder. Initially the pressure, volume and temperature were P1, V1, and T1. A spring with a spring constant …

Entropy of reversible process

We know that the freezing of water at meting point is a reversible process. Calculation of entropy for the system (the water) and surrounding for this freezing process is simply …

Entropy of irreversible process

Intuitively, we know that the freezing of water below meting point, e.g -10 ℃ occurs spontaneously. It means freezing of supercooled water is a irreversible process. Calculation of the entropy …

Exercise of calculating entropy

We can calculate the entropy changes between two states of different temperature if we know the heat capacities. When the pressure is constant, integration of Cp over temperature with respect …

Entropy change in chemical reactions

The entropy change for a chemical reaction among pure, crystalline substances is zero at the absolute zero K by the Third law of thermodynamics. Therefore, the entropy change of a …

The 3rd law

The third law is talking about the entropy of pure, perfectly crystalline materials at zero K. They have zero entropy at zero K, by the third law. Therefore, in classical …

Heat pump vs resistive heating

Heat pump vs resistive heating Which one is efficient? In the resistive heating, W = RI2 = Q when there is no loss. The maximum efficiency of resistive heating is …

Summary of week 3

This week, you learned the second law of thermodynamics. The second law is the entropy principle. The second law is concerned with the conversion of heat into work and the …

The week ahead

Welcome to the 4th week of the course.During this week, we are still talking about the second law of thermodynamics, but we are going be looking at its application to …

Heat engines

Heat engine is a system that convert thermal energy into mechanical energy. It is a traditional energy conversion system. Steam engine, internal combustion engine, and gasoline engine belong to the …

Heat engine P-V diagram

We have represented the heat engine cycle on a T-S diagram. Here we can express it on P-V diagram. At the high temperature source, the boiler, the fluid experience isothermal …

Refrigerators and heat pumps

Refrigerator and heat pump extract heat from the low temperature side, release heat to the high temperature side by doing work on the machine. Depending on the purpose of the …