And, again, this spontaneous process is also characterized by an increase in system entropy. This supports the common observation that placing hot and cold objects in contact results in spontaneous heat flow that ultimately equalizes the objectsвЂ™ temperatures. As for the previous example of matter dispersal, extrapolating this treatment to macroscopic collections of particles dramatically increases the probability of the uniform distribution relative to the other distributions. In 1865, Clausius named this property entropy ( S) and defined its change for any process as the following: Similar to other thermodynamic properties, this new quantity is a state function, and so its change depends only upon the initial and final states of a system. (a) Nicholas LГ©onard Sadi CarnotвЂ™s research into steam-powered machinery and (b) Rudolf ClausiusвЂ™s later study of those findings led to groundbreaking discoveries about spontaneous heat flow processes. Note that the idea of a reversible process is a formalism required to support the development of various thermodynamic concepts no real processes are truly reversible, rather they are classified as irreversible. The term reversible process refers to a process that takes place at such a slow rate that it is always at equilibrium and its direction can be changed (it can be вЂњreversedвЂќ) by an infinitesimally small change is some condition. This new property was expressed as the ratio of the reversible heat ( q rev) and the kelvin temperature ( T). In a later review of CarnotвЂ™s findings, Rudolf Clausius introduced a new thermodynamic property that relates the spontaneous heat flow accompanying a process to the temperature at which the process takes place. In 1824, at the age of 28, Nicolas LГ©onard Sadi Carnot ( Figure 1) published the results of an extensive study regarding the efficiency of steam heat engines.

Predict the sign of the entropy change for chemical and physical processes.

Explain the relationship between entropy and the number of microstates.

Since entropy change is expressed as heat divided by temperature, the units of entropy are calories perДegree (expressed as entropy units eu) or joules per kelvin, JK - 1 (expressed as EU). It is not possible to have a process in which the entropy of an isolated system decreases. The second law of thermodynamics may be stated in terms of entropy as follows: More interesting is the fact that entropy can be created but cannot be destroyed. An interesting fact about entropy is that, it is not a conserved quantity. Thus, if all the molecules in a given sample of a gas are made to move in the same direction with the same velocity, the entropy will be smaller than that in the actual situation in which the molecules move randomly in all directions. The entropy of the system remains constant in such a process.Д®ntropy is related to the disorder in the system. In an adiabatic reversible process, no heat is given out to the system. If the process is reversible, the change in entropy is defined as

In general, the temperature of the system may change during a process. If the system has a temperature T (in absolute scale) and a small amount of heat D Q is given to it, we define the change in the entropy of the system as In a given state of equilibrium, the system has a definite value of entropy.

Like pressure, volume, temperature and internal energy, we have another thermodynamic variable of a system, named entropy.

Symbol for entropy