Physics

The gas laws of Boyle, Charles law and Gay-Lussac do not apply to all gas conditions, so our analysis becomes more difficult. Therefore, presented the ideal gas model. Ideal gas does not exist in everyday life; the ideal gas is the just perfect form to facilitate analysis. The existence of this ideal gas concept also really helps us in reviewing the relationship between the three laws of gas.

The relationship among temperature, volume, and gas pressure

By referring to the three gas laws above, we can derive a more general relationship between temperature, volume, and gas pressure.

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The specific statements of the second law of thermodynamics can’t describe for all irreversible processes, so we need a general statement. This general statement is expected to explain all irreversible processes occurring in the universe. The general statement of the second law of thermodynamics was formulated in the mid-nineteenth century, through a quantity called entropy (S). Entropy was first introduced by Clausius and was formulated from the Carnot cycle (perfect caloric engine). According to Clausius, entropy changes are experienced by a system, when the system gets additional heat (Q) at a constant temperature, which is represented by the equation:

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Article about Coefficient of performance of the cooling machine

A cooling machine is a machine that takes heat from a low-temperature place, then transfers it to a high-temperature area. For this process to happen, the machine must do the work because the heat naturally flows from high temperature to low temperature. This is by Clausius’s statement:

It is impossible for a cooling machine to transfer heat from a low-temperature place to a high-temperature place, without work (Second law of thermodynamics—Clausius statement).

The machine works (W) to transfer heat, from low temperature (Q_L) to high temperature (Q_H). Based on conservation of energy, Q_L + W = Q_H.

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To find out how to increase the efficiency of the heat engine, a French scientist named Sadi Carnot (1796-1832) examined an ideal theoretical caloric machine in 1824. At that time, the first law of thermodynamics had not been formulated, nor the second law of thermodynamics. The first law has not been formulated because scientists do not yet know that heat is energy. After Joule and his colleagues experimented in the 1830s, scientists discovered heat is energy that moves due to temperature differences. So, the first law of thermodynamics was formulated after 1830. Sadi Carnot had been researching the theoretical ideal caloric engine in 1824. His research was actually to increase the efficiency of the steam engine. Most steam engines of that time were less efficient.

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To explain the irreversible thermodynamic processes, the scientists formulated the second law of thermodynamics. The second law of thermodynamics explains what processes can occur in the universe and what processes cannot happen. One scientist named R. J. E. Clausius (1822-1888) made the following statement:

Naturally, heat moves from high-temperature objects to low-temperature objects; naturally, heat does not proceed from low-temperature object to high-temperature object (Second law of thermodynamics—Clausius’s statement).

Clausius’s statement is one of the special statements of the second law of thermodynamics. It is called special statement because it only applies to one process just, related to heat transfer. Since this statement is not related to other processes, we need a more general statement. The development of a general statement of the second law of thermodynamics is based on the study about heat engine. Therefore, we discuss heat engine first.

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Article Thermodynamic processes : Isothermal Adiabatic Isochoric Isobaric

There are four thermodynamic processes, namely Isothermal, isochoric, isobaric and adiabatic processes.

Isothermal Process (constant temperature)

In an isothermal process, system temperature is kept constant. Theoretically, the analyzed system is an ideal gas. Ideal gas temperature is directly proportional to ideal internal gas energy (U = 3/2 n R T). T does not change, so U also does not change. Thus, if applied to the isothermal process, the first law of the thermodynamic equation becomes:

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Thermodynamic process

Heat (Q) is the energy that moves from one object to another because of the temperature difference. About systems and environments, heat is energy moving from system to environment or energy moving from environment to system, due to the temperature difference. If the system temperature is higher than the ambient temperature, heat will flow from the system to the environment. If the ambient temperature is higher than the system temperature, then heat flows from the environment to the system.

Heat (Q) is energy that moves due to the temperature difference, whereas work (W) is related to energy transfer through work. For example, if the system does work on the environment, then energy moves from system to environment. Conversely, if the environment does work on the system, then energy moves from environment to system.

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