Quantifying Entropy Changes in the Surroundings

We have seen that when a system exchanges heat with the surroundings, it changes the entropy of the surroundings. At constant pressure, we can use q ys to quantify the change in entropy for the surroundings (ASsurr)- In general, 

We can sununarize these three points with the proportionality  

Combining the proportionalities in Equations 17.1 and 17.2, we get the following general expression at constant tanperature  

For any chemical or physical process occurring at constant temperature and pressure, the entropy change of the surroundings is equal to the energy dispersed into the surroundings ( sys) divided by the temperature of the surroundings in kelvins. 

This equation provides insight into why exothermic processes have a tendency to be spontaneous at low temperatures— they increase the entropy of the surroundings. As temperature increases, however, a given negative q produces a smaller positive thus, exothermicity becomes less of a determining factor for spontaneity as temperature increases. 

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