Entropy Changes in the Universe

it is not just the entropy of the system that determines if a process is spontaneous, the entropy of the surroundings is also important. There are also examples of spontaneous processes in which A5 sys and ASgun- are both positive. The decomposition of hydrogen peroxide produces water and 

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Next, we account for the total entropy change in the universe o as a result of operating the process. 

The connection between entropy and the spontaneity of a reaction is expressed by the second law of thermodynamics The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process. Since the universe is made up of the system and the surroundings, the entropy change in the universe for any process is the sum of the entropy changes in the system (ASsys) and in the surroundings (ASsur,). Mathematically, we can express the second law of thermodynamics as follows ... 

The sum of the entropy changes in the system and the immediate surroundings is the entropy change in the universe we have the relation... 

The second law imposes an important limitation to all processes in nature The entropy change in the universe maybe zero or positive, but not negative. This requirement points a process always in the direction of equilibrium and has several important implications ... 

When a isothermal process occurs in a system that is not isolated, but is instead coupled to its surroundings, we cannot apply the second law of thermodynamics directly to the systan alone. Instead, we must consider the total entropy change in the universe, which from Equations 8.4 and 8.5 is given by... 

The entropy change of the surroundings, ASgurr has the same magnitude but opposite sign, because heat flows from the surroundings to the S5 tem. The net entropy change in the universe is therefore zero, as we would esqsect for a reversible process. 

The overall entropy change In the universe can then be calculated ... 

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