Entropy Changes in the Surroundings

We can use tabulated absolute entropy values to calculate the standard entropy change in a s stem, such as a chemical reaction, as just described. But what about the entropy change in the surroundings We encountered this situation in Section 19.2, but it is good to revisit it now that we are examining chemical reactions. 

We should recognize that the surroundings for any system serve essentially as a large, constant-temperature heat source (or heat sink if the heat flows from the system to the surroundings). The change in entropy of the surroundings depends on how much heat is absorbed or given off by the system. 

For an isothermal process, the entropy change of the surroundings is given by 

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As we have already emphasized, to use the entropy to judge the direction of spontaneous change, we must consider the change in the entropy of the system plus the entropy change in the surroundings ... 

If the system is neither closed nor thermally insulated, then the change in the entropy with time consists of two quantities of the time change in the entropy as a result of processes occurring within the system S and of entropy changes in the surroundings, caused by transfer of the entropy from the system in the reversible process Sc... 

Eor the heat exchange with the surroundings to occur reversibly (so that we can calculate the entropy change in the surroundings), we can imagine the gas to be in a vessel immersed in a large two-phase system (for example, solid-hquid) at... 

Self-Test 7.11B Calculate the entropy change in the surroundings when, 1.00 mol NH3(g) condenses at — 30°C. Take the enthalpy of vaporization of ammonia as 23.4 kJ-moC1. 

Furthermore, the entropy change in the surroundings, ASsurr, is related to the enthalpy change for the process by the equation ASsurr = —AH/T. 

Give an equation that relates the entropy change in the surroundings to the enthalpy change in the system. What is the sign of ASsurr for the following ... 

Calculation of the entropy produced in systems undergoing different flow processes (called irreversible processes) is key for considering steady-state systems. In order to measure the entropy produced in the system, we think of it as transported to the surroundings in a reversible manner and measure the entropy changes in the surroundings. From Eqs. (5) and (7),... 

In order to know whether or not a process in a closed system will occur spontaneously, it would be necessary to measure the entropy change in the surroundings (the rest of the universe) and obviously this is not possible. A device is needed to allow deduction of the entropy change of the universe from the process in the closed system. 

Calculating the entropy change in the surroundings would be hard, but because this entropy change is a consequence of an exchange of heat with the system, we can then write Equation 11-3 (assuming the process is reversible) ... 

First we will consider the entropy changes accompanying chemical reactions that occur under conditions of constant temperature and pressure. As for the other types of processes we have considered, the entropy changes in the surroundings are determined by the heat flow that occurs as the reaction takes place. However, the entropy changes in the system (the reactants and products of the reaction) can be predicted by considering the change in positional probability. 

Let rate of heat transfer Qj with respect to a particular part of the control surface be associated with Tt,j where subscript a, j denotes a temperature in the surroundings. The rate of entropy change in the surroundings as a result of this transfer is then —Qj /Taj. The minus sign converts Qj, defined with respect to the system, to a heat rate with respect to the surroundings. The third term in Eq. (5.20) is therefore the sum of all such quantities ... 

Liquid water at 325 K and 8000 kPa flows into a boiler at tlie rate of 10 kg s and is vaporized, producing saturated vapor at 8000 kPa. What is tlie maximum fraction of the heat added to the water in the boiler that can be converted into work in a process whose product is water at initial conditions, if Ftr = 300 K What happens to the rest of the heat What is the rate of entropy change in the surroundings as a result of the work-producing process In the system Total ... 

The Standard Entropy of Reaction Entropy Changes in the Surroundings Entropy Change and the Equilbrium State Spontaneous Exothermic and Endothermic Reactbns... 

Entropy Changes in the Surroundings The Other Port of the Total... 

What about the entropy change in the surroundings Although we will not prove it here, entropy changes in the surroundings are determined primarily by the flow of energy... 

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