And, on a lot of levels, it is. Entropy is an extensive state function. Entropy is zero in a reversible process; it increases in an irreversible process. But the big deal is that to some degree you can describe the universe in terms of entropy. Welcome to the first section in our unit on the second law of thermodynamics. Entropy is a function of the state of a thermodynamic system.It is a size-extensive quantity, invariably denoted by S, with dimension energy divided by absolute temperature (SI unit: joule/K). It is denoted by the letter S and has units of joules per kelvin. in terms of how much it changes during a process: $${\rm d}S=\frac{{\rm d}Q_{rev}}{T}$$ However, entropy is a state variable, so the question arises what the absolute entropy of a state might be. Entropy (S) is a thermodynamic quantity originally defined as a criterion for predicting the evolution of thermodynamic systems. And you might say okay this is all fun intellectual discussion, what's the big deal? The test begins with the definition that if an amount of heat Q flows into a heat reservoir at constant temperature T, then its entropy S increases by ΔS = Q/T. This is because the work done by or on the system and the heat added to or removed from the system can be visualized on the T-s diagram. entropyA thermodynamic property that is the measure of a system’s thermal energy per unit of temperature that is unavailable for doing useful work. Thermodynamics - Thermodynamics - Thermodynamic properties and relations: In order to carry through a program of finding the changes in the various thermodynamic functions that accompany reactions—such as entropy, enthalpy, and free energy—it is often useful to know these quantities separately for each of the materials entering into the reaction. Relation of Entropy With The Second Law of Thermodynamics. If system which is reversible from a state a to b, we will have . Entropy and the Second Law T-s diagram of Rankine Cycle. Entropy is calculated in terms of change, i.e., ∆S = ∆Q/T (where Q is the heat content and T is the temperature). Here we will look at some types of entropy which are relevant to chemical reactions. ... Entropy has a variety of physical interpretations, including the statistical disorder of the system, but for our purposes, let us consider entropy to be just another property of the system, like enthalpy or temperature. The value of this physical magnitude, in an isolated system, grows in the course of a process that occurs naturally. The second law of thermodynamics is the most fundamental law of physics. The Third Law of Thermodynamics means that as the temperature of a system approaches absolute zero, its entropy approaches a constant (for pure perfect crystals, this constant is zero). Information entropy is present whenever there are unknown quantities that can be described only by a probability distribution. The concept of entropy emerged from the mid-19th century discussion of the efficiency of heat engines. In this video, we're going to talk about the second law itself and this concept entropy just to state the second law right off the bat. When heat energy will be supplied to a thermodynamic system by a reversible process, the change in entropy in the thermodynamic system will be expressed as ∆S = Q/T, Temperature is constant. We try to explain it to ya!Why is it that disorder in our lives always seems to be increasing? It says that the entropy of an isolated system never decreases increases until the system reaches equilibrium. 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