How Suniv is affect by Ssys and Ssurr and TemperatureThe change of state for one mole of water from liquid to gas,H2O(l) H2O(g)For this process the entropy of the system increase;△Ssys has a positive sign “ + ”.How about the entropy change in the surroundings?△Ssurr : “ - ”When an endothermic process occurs in the system, heat flow from the surroundings to the system and the random motions of the atoms in the surroundings decrease, decreasing the entropy of the surroundings.The vaporization of water is an endothermic process.OK, then whether vaporization of water is a spontaneous process or not?(ΔSuniv = ΔSsys + ΔSsurr = “+” or “-”) It depends on the temperature: If the temperature > 100oC ΔSuniv > 0 If the temperature < 100oC ΔSuniv < 0How ΔSsurr is affected by tempThe central idea is that the entropy changes in the surroundings are primarily determined by heat flow.An exothermic process in the system increases the entropy of the surroundings, because the resulting energy flow increases the random motions in the surroundings.The significance of exothermicity as a driving force depends on the temperature at which the process occurs.This means that exothermicity (放熱性) is an important driving force for spontaneity.Two important characteristics of the entropy changes that occur in the surroundings:1. The sign of Δ Ssurr depends on the direction of the heat flow. (吸熱Δ Ssurr 0)2. the magnitude of Δ Ssurr depends on the temperature.Higher temperature energy provided by heat flow is more insignificantSummary:We can express Δ Ssurr in terms of the change in enthalpy Δ H for a process occurring at constant pressure, sinceIf the reaction is exothermic, Δ H has a negative sign, but since heat flows into the surroundings, Δ Ssurr is positive. Δ H and Δ Ssurr always have opposite sign.Sample Exercise 17.4 Determining Δ SsurrIn the metallurgy of antimony, the pure metal is recovered via different reactions, depending on the composition of the ore. For example, iron is used to reduce antimony in sulfide ores:Carbon is used as the reducing agent for oxide ores:Calculate Δ Ssurr for each of these reactions at 25℃ and 1 atm.SolutionWe usewhereFor the sulfide ore reaction,Note that Δ Ssurr is positive, as it should be, since this reaction is exothermic and heat flow occurs to the surroundings, increasing the randomness of the surroundings.For the oxide ore reaction,In this case Δ Ssurr is negative because heat flow occurs from the surroundings to the system.TABLE 17.3 Interplay of Δ Ssys and Δ Ssurr in Determining the Sign of Δ Suniv