When does the third law of thermodynamics apply? (2 marks)Īns. The law also supports examining chemical and phase equilibrium.The behavior of solids is determined by the law at low temperatures.Application of the law is helpful in calculating the properties of thermodynamics.The process continues naturally in the direction of higher randomness or disorder.Entropy is regarded as an extensive property.The entropy of mixing with non-reacting substances, the system is invariably higher.Therefore, once again the possibility of the system reaching absolute zero is eliminated. In such a situation the heat energy comes from an external source outside the system. In the process to reach absolute zero, the system tends to capture heat energy from the external environment and thus, absolute zero temperature can never be achieved.Īccording to the first law of thermodynamics, the possibility of creation and destruction of energy is completely ruled out. As per the second law, it has been established that the spontaneous movement of heat from a colder medium to a hotter medium is not possible. This will restrict the movement of the molecules and result in lower entropy.Ĭontradiction with the Other Laws of ThermodynamicsĬontrary to the third law of thermodynamics that determines absolute zero as a state, the second law of thermodynamics rules out the fact that temperature can actually become zero. However, once the steam or water vapor cools down below 100 degrees Celsius it will change into water. The temperature of any gaseous form of water such as steam or water vapor is high and the molecules inside these gases move randomly. Here, Cp is represented as the heat capacity of the substance at constant pressure where the value is considered as constant in the 0 to T K range. However, a simpler representation for the absolute entropy of a solid at temperature T is stated below: This integral value can be found by plotting the graph of Cp/ T versus T followed by determining the area of this curve starting from 0 to T. In the case of solids, if S0 is the entropy at 0 K and S is the entropy at T K, then:īased on the third law of thermodynamics, S0 = 0 at 0 K, thus, Such conclusions are derived from the measurements of the heat capacity of the substance. One of the prime applications of the third law of thermodynamics is that it supports calculating the absolute entropy at any particular temperature (T). Application of the Third Law of Thermodynamics Therefore, a perfect crystal entropy at absolute zero temperature is zero. While zero is selected as the system’s initial entropy, its value of ‘S’ can be obtained as follows: In the case of a perfect crystal with only 1 unique ground state, Ω = 1. Ω specifies the total number of microstates consistent with the macroscopic configuration of the system.In statistical mechanics the equation representing the third law of thermodynamics is as follows: Third Law of Thermodynamics - Mathematical Explanation The SI units representing entropy are J/K (joules/degrees Kelvin). An isothermal process states when the heat change (Q) is divided by the absolute temperature (T) it results in the change in entropy (ΔS).Chemical complexity results in higher entropy.Hard and brittle materials have lower entropy compared to pliable solids such as metals.
Dissolving gas in water lowers the entropy.Mixing of solids and liquids results in higher entropy.Melting and evaporation lead to higher entropy.The more the energy is dispersed the greater would be the entropy. While work is done the usable energy changes to unusable energy. Nature plays a vital role in creating disorder compared to order, like aging, rusting, decaying, etc. Any variation in entropy associated with a process from its initiation to its end is denoted by ΔS. The microstate wherein the system has the lowest energy is termed as the ground state of the system. It is relative to the number of microstates (a definite microscopic state possessed by a system) that a system can access, which means, the more microstates the closed system has, the higher will be its entropy. The symbol ‘S’ signifies entropy which is a degree of randomness or disorder in a closed system.
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