Thermodynamics Chapter 6: Second Law

A system or body that can absorb or release a large amount of heat without significantly changing its temperature.

A thermal energy reservoir that supplies heat to a system.

A thermal energy reservoir that absorbs heat from a system.

A device that converts thermal energy (heat) into mechanical work.

The process of transferring heat from a high-temperature source to a low-temperature sink, in order to produce work.

The amount of heat that is converted into work by a heat engine.

The amount of heat that is rejected by a heat engine to a low-temperature sink.

The ratio of work output to heat input in a heat engine.

The Second Law of Thermodynamics states that heat cannot spontaneously flow from a colder object to a hotter object. This means that heat transfer always occurs from a region of higher temperature to a region of lower temperature.

The First Law of Thermodynamics deals with energy conservation, stating that energy cannot be created or destroyed, only transformed from one form to another.

Many real-world processes, like the conversion of electric energy to heat, can occur spontaneously. However, the reverse process, converting heat into an equivalent amount of electric energy, cannot happen spontaneously.

The Second Law of Thermodynamics explains why energy conversion processes are not 100% efficient. Some energy is always lost as unusable heat, limiting the amount of useful work that can be extracted.

Examples like a paddle wheel stirring a fluid or a car driving uphill illustrate that while the First Law is satisfied, the reverse processes, like raising the mass by heat transfer to the paddle wheel, are not possible. This demonstrates the irreversibility of real-world processes.

The Second Law of Thermodynamics is a fundamental principle in engineering, guiding the design and optimization of systems. It helps us understand limitations, maximize efficiency, and develop sustainable technologies.

The Second Law of Thermodynamics introduces the concept of entropy, a measure of disorder or randomness in a system. The entropy of a closed system always increases over time, implying more disorder.

The Second Law of Thermodynamics has profound implications for the universe as a whole, indicating an eventual state of maximum entropy, known as heat death, where all energy will be evenly distributed, leading to a state of thermal equilibrium.

Processes are irreversible; they proceed in a specific direction, usually towards equilibrium. They can't be reversed without external work.

The First Law of Thermodynamics only deals with the conservation of energy. It doesn't provide insights into the feasibility of a process.

The Second Law plays a crucial role in determining the performance of various engineering systems like heat engines and refrigerators.

Energy has two critical aspects: quantity and quality. The First Law focuses on quantity, while the Second Law examines the quality and degradation of energy during a process.

A thermal energy reservoir acts as a source or sink of heat at a constant temperature. It has an immense capacity to absorb or release heat without significant temperature change.

Thermal energy capacity is a property that signifies how much thermal energy a substance can store or release for a given temperature change.

Specific heat is the amount of heat required to raise the temperature of one unit mass of a substance by one degree.

The second law of thermodynamics states that heat cannot spontaneously flow from a colder body to a hotter body. This means that heat engines, which convert heat to work, can never be 100% efficient because some energy must be lost as waste heat.

In a heat engine, the high-temperature medium is where heat is absorbed from. The low-temperature medium is where heat is rejected to.

The thermal efficiency of a heat engine is calculated as the ratio of the work done by the engine to the amount of heat it absorbs. It can be expressed as ηth = Work/QH, where ηth is the thermal efficiency, Work is the work done, and QH is the heat absorbed from the high-temperature medium.

In a steam power plant, the condenser is the device where the waste heat is rejected to the environment. This waste heat is energy that is not converted into useful work.

While it sounds like a good idea, removing the condenser from a power plant would not save energy. The second law of thermodynamics dictates that some heat must be rejected to the environment, otherwise the engine would not be able to function. Removing the condenser would violate this law and disrupt the cycle.

The thermal efficiency of a heat engine is usually quite low, meaning much of the energy put into the engine is lost as waste heat. Even the most efficient engines today lose almost half of the energy supplied.

It is impossible to create a device that can transfer heat from a colder object to a hotter object without any external work being done.

The Clausius statement says that a refrigerator cannot function without an external power source, like an electric motor.

The net effect of a refrigerator's operation is that it consumes energy in the form of work, in addition to transferring heat from a colder body to a warmer one.

The Kelvin-Planck statement states that a heat engine cannot operate with 100% efficiency and therefore cannot convert all heat into work.

If we combined a heat engine that violates the Kelvin-Planck statement with a refrigerator capable of transferring heat from a colder to a hotter reservoir without any external work, we could create a system that violates the Clausius statement.

The Kelvin-Planck and Clausius statements are equivalent in their implications. A device violating one statement automatically violates the other.

Any device that violates the Kelvin-Planck statement necessarily violates the Clausius statement, and vice versa.

A machine that violates either the First or Second Law of Thermodynamics, attempting to create energy from nothing or extract work from a single temperature source.

A perpetual-motion machine that violates the First Law of Thermodynamics by claiming to create energy from nothing.

A perpetual-motion machine that violates the Second Law of Thermodynamics by claiming to extract work from a single heat source.

A system that continuously supplies energy without receiving any input, violating the First Law of Thermodynamics.

An invention that aims to improve power plant efficiency by eliminating the condenser, claiming to transfer all heat to steam and convert it into work.

An example of a PMM2, where a power plant without a condenser is proposed, attempting to extract work from a single heat source (the furnace).

A system that operates in a cycle, performing work while exchanging heat with only a single heat source.

A system that violates the Second Law of Thermodynamics by transferring heat from a lower temperature to a higher temperature without external work input.