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Thermodynamics is a discipline of physics concerned with the concepts of heat and temperature and the conversion of heat to various kinds of energy. Thermodynamics is a science that is studied at a microscopic level. It is concerned with the bulk system and does not address the molecular structure of matter; in fact, its notions and rules were developed in the nineteenth century, far before the molecular picture of matter had become firmly established. A microscopic description of a gas, for example, would entail identifying the coordinates and velocity of the enormous number of molecules that make up the gas. The molecular distribution of velocities is not shown in detail in the description and kinetic theory of gases. Thermodynamic descriptions of gases, on the other hand, omit molecular descriptions entirely, instead of specifying the state of gas using microscopic variables such as pressure, volume, temperature, mass, and composition, all of which can be felt and measured.
Entropy
Entropy is a measure of a system’s dysfunction. It expresses the amount of energy that is not available for work. The higher the entropy of a system, the less energy is available to conduct work in that system. Although all sources of energy can be employed to perform work, it is impossible to utilize all of the available energy. Not all of the energy conveyed by heat can be transformed into work, and part of it is wasted as waste heat or heat that is not used to perform work. In Thermodynamics, energy availability is critical; in fact, the field arose from efforts to transform heat to work, as done by engines.
The SI unit of entropy is joules/kelvin (J/K).
The equation for the change in entropy ∆S is
∆s=Q/T
Where Q is the heat that transfers energy during the process
T is the absolute temperature (Thermodynamics defines temperature as a quantity different from kinetic theory or mechanics. The temperature measurement of zero is particularly important in thermodynamics. So, any thermometric scale on which a reading of 0 corresponds to the theoretical absolute zero temperature is known as Absolute Temperature).
Laws of thermodynamics
- First law of thermodynamics
The first law of thermodynamics is the universal law of energy conservation that applies to all systems. “The total heat energy change in every system is the sum of the internal energy change and the work done,” says this law.
When a certain amount of heat, dQ, is applied to a system, a portion of it is used to increase internal energy, dU, and a portion is utilized to perform external work, dW, resulting in dQ = dU + dW.
The specific heat capacity of gases is determined by the procedure or conditions in which heat capacity is transferred. For gas, there are primarily two types of specific heat capacities. Specific heat capacity at constant volume and specific heat capacity at constant pressure are the two types of specific heat capacity.
A relationship between two primary specific temperatures of an ideal gas may be found using the First Law of Thermodynamics. Cp-Cv = R, according to the relationship
The molar specific temperatures Cp and Cv are calculated under constant pressure and constant volume conditions, respectively.
Cp > Cv indicates that a gas’s specific heat capacity at constant pressure is greater than its specific heat capacity at constant volume. The reason for this is that when heat is delivered to a gas at a constant volume, the gas does not work against the external pressure, and all of the energy is used to raise the gas’s temperature.
When heat is applied to gas at constant pressure, the volume of the gas rises, and the heat energy is used to raise the temperature of the gas as well as to perform work against the external pressure.
The thermal equivalent of the effort done in expanding the gas against the external pressure is the difference between the two specific heats.
- Second law of thermodynamics
The second law of thermodynamics is a principle that forbids certain behaviors that are consistent with the first rule of thermodynamics.
The two statements of the second law of thermodynamics are as follows.
Kelvin-Planck Statement: It is impossible to build a cycle engine that extracts heat from a hot body and converts it totally into work without any alteration, i.e., 100 percent conversion of heat into work is impossible.
A heat engine is a device that causes a system to go through a cyclic process that converts heat to work. A heat engine is made up of three parts: a heat source, a heat sink, and a working substance.
Carnot’s Engine is a fictional character. He proposed a hypothetical engine that operates between two temperatures and uses a cyclic/reversible process. Its efficiency is given by =1-T2/T1, where T1 is the temperature of the source and T2 is the temperature of the sink and is independent of the working substance.
According to Carnot’s theorem, no engine can have a higher efficiency than Carnot’s engine while working between two given temperatures T1 and T2 of the hot and cold reservoirs, respectively, and (b) the efficiency of the Carnot engine is independent of the nature of the working substance.
Principle of entropy
- The entropy of an isolated system (universe) that goes through a specific process is always equal to zero (in the case of reversible) or greater than zero.
- Heat always travels from a hot surface to a cold surface.
- The degree of randomness is measured by entropy, which is a state attribute. whereas the entropy of a system can be negative, the entropy of the cosmos as a whole is always positive or zero (in the case of reversible processes)
Conclusion
Thermodynamics is the branch of physics that studies the translation of heat into other kinds of energy and vice versa.
The science of thermodynamics is a macroscopic one. It focuses on bulk systems rather than the molecular structure of stuff. Energy cannot be created or destroyed in an isolated system, according to the first law, often known as the Law of Conservation of Energy. The entropy of any isolated system always increases, according to the second rule of thermodynamics. Entropy can be conceived of as a metric for energy dispersion. It calculates the amount of energy that has been diffused in a process. Any energy flow is always from high to low. As a result, entropy is always increasing.
