What is Entropy in Physics? Definition, Explanation, Thermodynamic

The concept of entropy was introduced into the study of thermodynamic by Rudolph Clausius in 1856 to give a quantitative basis for the second law. It provides another variable to describe the state of a system to go along with pressure, volume, temperature and internal energy. If a system undergoes a reversible process during which it absorbs a quantity of heat ∆Q at absolute temperature T, then the increase in the state variable called entropy S of the system is given by

∆S = ∆Q/T

What is Entropy?    

The measurement of disorderness of a system is called its Entropy. It is denoted by ∆S. It’s SI unit is Jk^-1.

Like potential energy or internal energy, it is the change in the entropy of the system which is important. Change in entropy is positive when heat is added and negative when heat is removed from the system. Suppose, an amount of heat Q flows from a reservoir at temperature T₁ through a conducting rod to reservoir at temperature T₂ when T₁ > T₂. The change in entropy of the reservoir, at temperature T₁, which loses heat, decreases by Q/T₁ and of the reservoir at temperature T₂, which gains heat, increase by Q/T₂. As T₁ > T₂ so Q/T₂ will be greater than Q/T₁ i.e. Q/T₂ > Q/T₁.

Hence, net change in entropy = Q/T₂ – Q/T₁is positive. It follows that in all natural processes where heat flows from one system to another, there is always a net increase in entropy.

Entropy According to 2^nd Law of Thermodynamics:

“If a system undergoes a natural process, it will go in the direction that causes the entropy of the system plus the environment to increase.”

It is observed that a natural process tends to proceed towards a state of greater disorder. Thus, there is a relation between entropy and molecular disorder.

Example # 1:          

An irreversible heat flow from a hot to cold substance of a system increases disorder because the molecules are initially sorted out in hotter and cooler regions. This order is lost when the system comes to thermal equilibrium. Addition of heat to a system increases its disorder because of increase in average molecular speeds and therefore, the randomness of molecular motion. Similarly, free expansion of gas increases its disorder because the molecules have greater randomness of position after expansion than before.

We can conclude that only those processes are probable for which entropy of the system increases or remains constant. The process for which entropy remains constant is a reversible process; whereas for all reversible processes, entropy of the system increases. Every time entropy increases, the opportunity to convert some heat into work is lost.

Example # 2:

There is an increase in entropy when hot and cold waters are mixed. Then warm water which results cannot be separated into a hot layer and a cold layer. There has been no loss of energy but some of the energy is no longer available for conversion into work. Therefore, increase in entropy means degradation of energy from a higher level where more work can be extracted to a lower level at which less or no useful work can be done. The energy in a sense is degraded, going from more orderly form less orderly form, eventually ending up as thermal energy.

In all real processes where heat transfer occurs, the energy available for doing useful work decreases. In other words, the entropy increases. Even if the temperature of the system decreases, thereby decreasing the entropy, it is at the expense of net increase in entropy for some other system. When all the systems are taken together as the universe, the entropy of the universe always increases.

Environmental Crisis as Entropy Crisis:    

The second law of Thermodynamics provides us the key for both understanding Allman mental crisis add grandstanding how we must deal with this crisis. From a human standpoint the environmental prize results from our attempts to order nature for our comforts and greed. from a physical standpoint however the environmental crisis is an entropy or disorder crisis resulting from are futile efforts to ignore the second law of Thermodynamics, according to which, any increase in the order in a system will provide an even greater increase in entropy or disorder in the environment. An individual impact may not have a major consequence but an impact of large number of all individuals’ disorder producing activities can affect the overall life support system. The energy possesses we use are not very efficient.

As a result, most of the energy is lost as heat to the environment. Although we can improve the efficiency but second law eventually imposes an upper limit on efficiency improvement. Thermal pollution is an inevitable consequence of second law of thermodynamics and heat is the ultimate death of any form of energy. The increase in thermal pollution of the environment means increase in entropy and that causes great concern. Even small temperature changes in the environment can have significant efforts on metabolic rates in plant and animals. this can cause serious disruption of the overall ecological balance. In addition to thermal pollution the most energy transformation processes such as heat engine use for transportation and for energy generation cause air pollution.

In effort, all forms of energy production have some undesirable effects and in some cases all problems cannot be anticipated in advance. The imperative from thermodynamics is that whenever you do anything, be sure to take into account it's present and possible future impact on your environment. this is and ecological imperative that we must consider now if we are to prevent a drastic degradation of life on our beautiful bar fragile earth.