Entropy change surroundings

So the stationary state is maintained through the decrease in entropy exchanged between the system and its surrounding. Entropy change inside an elementary volume by irreversible phenomena is the local value of the sum of entropy increments. By the second law of thermodynamics, the entropy production c/,5 is always positive for irreversible changes and zero for reversible changes. 

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

Second Law of Thermodynamics. The entropy change of any system together with its surroundings is positive for a real process, approaching zero as the process approaches reversibiUty ... 

The entropy change of any. system and its. surroundings, considered together, re.sulting from any real proce.s.s is positive, approaching zero when the proce.s.s approaches reversibility. 

The entropy change of the surroundings, found by integration of Eq. (4-3), is AS = QJTa, whence... 

Since heat transfer with respec t to the surroundings and with respect to the system are equal but of opposite sign, = —Q. Moreover, the second law requires for a reversible process that the entropy changes of system and surroundings be equalbut of opposite sign AS = —AS Equation (4-356) can therefore be written Q = TcAS In terms of rates this becomes... 

The relationship between entropy change and spontaneity can be expressed through a basic principle of nature known as the second law of thermodynamics. One way to state this law is to say that in a spontaneous process, there is a net increase in entropy, taking into account both system and surroundings. That is,... 

Notice that the second law refers to the total entropy change, involving both system and surroundings. For many spontaneous processes, the entropy change for the system is a negative quantity. Consider, for example, the rusting of iron, a spontaneous process ... 

AS° for this system at 25°C and 1 atm can be calculated from a table of standard entropies it is found to be —358.4 J/K. The negative sign of AS° is entirely consistent with the second law. All the law requires is that the entropy change of the surroundings be greater than 358.4 J/K, so that ASunIverse > 0. 

In principle, the second law can be used to determine whether a reaction is spontaneous. To do that, however, requires calculating the entropy change for the surroundings, which is not easy. We follow a conceptually simpler approach (Section 17.3), which deals only with the thermodynamic properties of chemical systems. 

Adiabatic processes are examples of (d). If a mole of ideal gas is allowed to expand adiabatically into an evacuated bulb to twice its initial volume, the entropy of the gas increases by 5.76 J K-1 mol-1. No entropy change occurs in the surroundings, since there is no exchange of heat. Hence, 5.76 J K-1 mol-1 is the net increase in entropy in the universe. 

Entropy is an important concept in chemistry because we can use it to predict the natural direction of a reaction. However, not only does the entropy of the reaction system change as reactants form products, but so too does the entropy of the surroundings as the heat produced or absorbed by the reaction enters or leaves them. Both the entropy change of the system and that of the surroundings affect the direction of a reaction, because both contribute to the entropy of the universe. We explore the contribution of the system in this section and the contribution of the surroundings in the next section. 

The system ot interest and its surroundings constitute the isolated system to which the second law refers (Fig. 7.15). Only if the total entropy change,... 

We can use Eq. 1 to calculate the entropy change of the surroundings, provided that we assume that the surroundings are so large that their temperature and pressure remain constant. If the enthalpy change of the system is AH, then, for heat transfers at constant pressure, gSLlrr = —AH. We can now use Eq. 1 to write... 

Self-Test 7.14A Calculate the entropy change of the surroundings when 1.00 mol H20(l) vaporizes at 90°C and I bar. Take the enthalpy of vaporization of water as 40.7 kj-mol. ... 

Self-Test 7.14B Calculate the entropy change of the surroundings when 2.00 mol NHj(g) is formed from the elements in their most stable forms at 298 K. 

FIGURE 7.17 (a) In an exothermic process, heat escapes into the surroundings and increases their entropy, (b) In an endothermic process, the entropy of the surroundings decreases. The red arrows represent the transfer of heat between system and surroundings, and the green arrows indicate the entropy change of the surroundings. 

The entropy change of the surroundings due to a process taking place at constant pressure and temperature is equal to —AH/T, where AH is the change in enthalpy of the system. 

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 ... 

The standard entropy of vaporization of benzene is approximately 85 J-K -mol-1 at its boiling point, (a) Estimate the standard enthalpy of vaporization of benzene at its normal boiling point of 80.°C. (b) What is the standard entropy change of the surroundings when 10. g of benzene, CfiHfi, vaporizes at its normal boiling point ... 

The following pictures show a molecular visualization of a system undergoing a spontaneous change. Account for the spontaneity of the process in terms of the entropy changes in the system and the surroundings. 

Entropy change of the surroundings for a process in a system with enthalpy change AH ... 

The problem asks for the total entropy change, which includes A S for the water and A S for the freezer compartment. When water freezes, heat flows from the water to its surroundings, the freezer compartment (see Eigure 14-61. Thus, q is negative for the water, whose entropy decreases. At the same time, q is positive for the freezer compartment, whose entropy increases. 

When calculating entropy changes, be careful about the sign of q, use the appropriate temperatures, and sum the changes for system and surroundings. 

Equation gives the total entropy change A — A jS ystem + A Fjmygmjgjggs We can define the HFC as the system and the contents of the refrigerator as the immediate surroundings ... 

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