The Third Law Of Thermodynamics: Exempt Materials Explained

The third law of thermodynamics states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value as its temperature approaches absolute zero. This means that at absolute zero, the system must be in a state with the minimum possible energy. The third law was formulated by Walther Nernst between 1906 and 1912 and is therefore often referred to as Nernst's theorem or the Nernst-Simon heat theorem.

The third law applies to perfect crystalline substances, which have a unique state (the ground state) with minimum energy. In such cases, the entropy at absolute zero is exactly zero. However, if the system does not have a well-defined order, there may be some finite entropy as the temperature approaches zero.

While the third law provides a reference point for determining the absolute entropy of a substance at any temperature, it does not apply to non-crystalline solids such as glass. These materials can retain significant entropy at absolute zero due to their disordered structure.

Non-crystalline solids (glasses)

The third law of thermodynamics states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value when its temperature approaches absolute zero. This constant value is independent of other parameters, such as pressure or applied magnetic fields. At absolute zero, the system exists in a state of minimum energy, known as the ground state.

Non-crystalline solids, such as glasses, are exceptions to this law. In these materials, there may be some residual entropy remaining at absolute zero. This is because non-crystalline solids lack a well-defined order and may become locked into a configuration with non-minimal energy. Additionally, they may have multiple minimum energy states, preventing them from reaching zero entropy.

Glasses, specifically, retain significant entropy at absolute zero because they are large collections of nearly degenerate states, in which they become trapped out of equilibrium. This means that a substantial amount of configurational entropy is frozen into the structure of glasses, which has been confirmed by experiments.

The third law, originally formulated by Walther Nernst, has been modified over the years by scientists such as Gilbert N. Lewis and Merle Randall, who stated that:

> If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has a finite positive entropy; but at the absolute zero of temperature, the entropy may become zero, and does so become in the case of perfect crystalline substances.

This statement suggests that while the entropy of a perfect crystal will reach zero at absolute zero, non-crystalline solids like glasses may not, as they do not have a unique ground state.

Liquid mercury under ambient pressure

The third law of thermodynamics states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value when its temperature approaches absolute zero. At absolute zero, the system must be in a state with the minimum possible energy.

Mercury is the only metal that is a liquid at room temperature and pressure. In its liquid state, mercury atoms have enough thermal energy to overcome the rigid metallic bonds that confine most metals to a solid state at room temperature.

The third law of thermodynamics links temperature and entropy. Entropy is related to the number of accessible microstates, and there is typically one unique state (called the ground state) with minimum energy. In such a case, the entropy at absolute zero will be exactly zero.

The third law was developed by the German chemist Walther Nernst between 1906 and 1912, and it is often referred to as the Nernst heat theorem. An alternative version of the third law was proposed by Gilbert N. Lewis and Merle Randall in 1923, which states that:

> If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has a finite positive entropy; but at the absolute zero of temperature, the entropy may become zero, and does so become in the case of perfect crystalline substances.

The third law provides an absolute reference point for determining the entropy of a system at any other temperature.

Disordered solid solutions or amalgams

The third law of thermodynamics states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value when its temperature approaches absolute zero. This constant value cannot depend on any other parameters characterizing the system, such as pressure or applied magnetic field. At absolute zero, the system must be in a state with the minimum possible energy.

Entropy is related to the number of accessible microstates, and there is typically one unique state (called the ground state) with minimum energy. In such a case, the entropy at absolute zero will be exactly zero.

In the context of the third law of thermodynamics, a "perfect crystal" refers to a highly ordered crystalline lattice with no impurities and a well-defined position for each atom, ion, or molecule. This excludes amorphous solids like glass, which lack an ordered crystalline structure and have not achieved thermodynamic equilibrium.

The third law provides an absolute reference point for determining the entropy of a substance at any temperature, which is particularly useful for calculating the entropy change in chemical reactions.

Random elemental isotopic abundances

The third law was formulated by Walther Nernst between 1906 and 1912 and is often referred to as the Nernst heat theorem. It is important to note that the third law does not claim that entropy becomes zero as temperature approaches absolute zero. This is a common misconception. Instead, it states that entropy approaches a constant value, which is often close to zero, especially for pure crystalline substances.

However, there are several examples where the entropy remains significant even at absolute zero. These include liquid mercury at ambient pressure, disordered solid solutions or amalgams, and random elemental isotopic abundances. In these cases, the system does not reach a unique ground state, and there may be multiple configurations or microstates with minimum energy.

The third law has important implications for the calculation of absolute entropy and provides a reference point for determining the entropy of a substance at any temperature. It also highlights the unattainability of absolute zero temperature, as an infinite number of steps would be required to reach this state.

Ferromagnetic materials

The third law of thermodynamics states that the entropy of a perfect crystal at a temperature of zero Kelvin (absolute zero) is zero. Entropy, denoted by 'S', is a measure of the disorder or randomness in a closed system. It is directly related to the number of microstates (fixed microscopic states) that can be occupied by a system.

The third law was developed by German chemist Walther Nernst between 1906 and 1912, and it is often referred to as the Nernst heat theorem. This law provides an absolute reference point for determining the entropy of a closed system at any other temperature.

The third law has several implications and alternative formulations, including:

• It is not possible for any process to bring the entropy of a system to zero in a finite number of operations.
• The exchange of energy between two thermodynamic systems that make up an isolated system is bounded.
• It is impossible to start from a positive temperature state and adiabatically reach a state of zero temperature.

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