![]() ![]() for all the spontaneous processes, the total entropy change of the system is positive.We face a colossal energy storage problem with analysts predicting a more than 120-times increase in global energy storage needs by 2040 1. The complete conversion of heat into work is impossible without leaving some effect elsewhereĪll spontaneous processes are accompanied by a net increase of entropy i.e. Without the help of an external agency, a spontaneous process cannot be reversed.įor Ex: Heat cannot by itself flow from a colder to hotter body. If S total is negative, the direct process is non-spontaneous whereas the reverse process may be spontaneous.ġ)If ΔS total or ΔS universe is positive, the process is spontaneous.Ģ)If ΔS total or ΔS universe is negative, the direct process is non-spontaneous whereas the reverse process may be spontaneousģ)If ΔS total or ΔS universe is zero, the process is in equilibrium.Īll spontaneous processes are thermodynamically irreversible. The entropy of the system at equilibrium is maximum and there is no further change in entropy i.e. ΔS =0. The randomness and hence the entropy keeps on increasing till ultimately an equilibrium is reached. These processes involve exchange of matter and energy with the surrounding.Hence they are not isolated systems.įor these processes, we have to consider the total entropy change of the system and the surrounding.įor the process to be spontaneous, ΔS total must be positive.įor all spontaneous processes, the total entropy change ( ΔS total ) must be positive. fro these processes, entropy change is positive.Ģ)Reaction taking place between a piece of marble or sodium hydroxide and Hydrochloric acid in an open vessel. These processes are accompanied by increase of randomness and hence increase of entropy i.e. These processes do not involve any exchange of matter and energy with the surrounding.Hence they are isolated systems. If we compress the gas isothermally from volume V 2 to V 1, heat q rev will be given out by the system and absorbed by the reservoir so that ΔS = − q rev / T and ΔS = q rev / T Total change in entropy ΔS 1 = ΔS sys + ΔS res = q rev / T + ( − q rev / T ) =0 The system absorbs heat q isothermally and reversibly at temperature T and expands from volume V 1 to V 2.Īs equivalent amount heat is lost by the reservoir, The physical significance of entropy is that many processes which are accompanied by an increase of entropy are also accompanied by an increase of randomness or disorder.Ĭonsider a system consisting of a cylinder containing a gas at fitted with frictionless and weightless piston and placed in contact with the large heat reservoir. The units of entropy change are cal/K/mol in CGS system and joules/K/mol in S.I. This shows that entropy change is inversely proportional to temperature.Įntropy change during a process is defined as the amount of heat ( q ) absorbed isothermally and reversibly divided by the absolute Temperature ( T ) at which the heat is absorbed. More the heat absorbed ,greater is the disorder.Ģ) For the same amount of heat absorbed at low temperature, the disorder is more than at high temperature. ΔS = S 2 -S 1 = ∑S products – ∑S reactantsġ) When a system absorbs heat ,the molecules start moving faster because kinetic energy increases. The change in its value during a process, is called the entropy change. ![]() Solid state has the lowest entropy, the gaseous state has the highest entropy and the liquid state has the entropy in between the two.Įntropy is a state function. The greater the randomness, higher is the entropy. Entropy is a measure of randomness or disorder of the system. ![]()
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