ENTROPY AND THE SECOND LAW OF THERMODYNAMICS

1 ENTROPYANDTHE SECOND LAW OF THERMODYNAMICSThe contents of this module were developed under grant award # P116B-001338 from the Fund for the Improve-ment of Postsecondary Education (FIPSE), United States Department of , those contents do not necessarily represent the policy of FIPSE and the Department of Education, and you should not assume endorsement by the Federal STEPHEN THOMPSONMR. JOE STALEYE nergy and entropyfl ow out of the system decreases in entropyAdditional Energy is Additional Energy is Additional Energy is Additional Energy is added to the system,added to the system,added to the system,EnergyReservoirTIMEThe system consists of the red circles in the blue AND THE SECOND LAW OF THERMODYNAMICSCONTENTS2 Introduction To Entropy2 Energy Disperses3 Entropy4 Enthalpy And Entropy5 Thermal Entropy6 Confi gurational Entropy7 Confi gurational ENTROPY .

2 Cellular Representation8 Confi gurational ENTROPY : Combined Representation9 Dispersible Energy10 Diffusion11 Liquid Crystal12 Salt Dissolving In Water13 The Pfeffer Tube14 The SECOND Law Of Thermodynamics15 Gibbs Free Energy16 Gibbs Free Energy And Temperature17 Gibbs Free Energy And Temperature18 How ENTROPY Can Decrease (In A System)19 Periodic ENTROPY Of The ElementsINTRODUCTION TO ENTROPYTimeTimeStyrofoamMetalTimeIn the experiments pictured above, the blue repre-sents cooling, or loss of thermal the evaporation of water exothermic or What is the evidence?

3 If it is endothermic, how can it proceed spontane-ously in the isolated system where the petri dish is placed on styrofoam?TimeTimeTimeSpontaneous endothermic reactions do occur and that means that there must be another factor than enthalpy involved. Scientists call this factor have personal experience of ENTROPY when we feel the coolness of DISPERSESTIMEIn the picture above the red ink represents energy. As time proceeds there is the same amount of ink (energy) but it spreads out, becomes less concentrated, disperses.

4 ENTROPY is the measure of this dispersalThe SECOND law of THERMODYNAMICS says that the oppo-site change is impossible in an isolated AND THE SECOND LAW OF THERMODYNAMICS2 ENTROPY AND THE SECOND LAW OF THERMODYNAMICSENTROPYE0E1E2E3E0E1E2E3oox ooyoozoozooyooxooxooyoozooxooyoozE0E1E2E 3ooxooyoozooxooyoozooxooyoozooxooyoozoox ooyoozooxooyoozSuppose three molecules have a total of three quanta of energy to share between them and that each mol-ecule can occupy one of four energy states requiring zero, one, two or three quanta to 1 has one possibility, that is,one 2 has threepossibilities, that is,three 3 has six possibilities, six each microstate is as likely to be occupied as any other is the most likely macrostate to be occupied?

5 Suppose that the system shifts from one microstate to another at random times, what proportion of the time will the system be in macrostate 1? in macro-state 2? in macrostate 3?Assume the three quanta of energy are distributed among four molecules. How many macrostates will four molecules. How many macrostates will fourthere be and how many microstates will there be for each macrostate? Suggestion: use drawings like the ones above to fi gure this four quanta of energy are distributed among four molecules with four available energy states.

6 How many macrostates will there be and how many microstates to each macrostate?In chemistry there are several different means by which energy can be dispersed and thus ENTROPY created. These include:1. The number of molecules among which the ENTROPY can be rest of these examples refer to the same number of molecules:2. The volume of space which the molecules can The freedom with which the molecules can move about that space, , the difference between a solid and a liquid. This would include the freedom to change location and, in the case of nonspherical molecules, the freedom to change oritentation or The amount of energy available, which determines the range of energy states which the molecules can The complexity of the molecules, which determines how many rotational and vibrational states they can have.

7 We have described several sources of ENTROPY . You describe several conditons that can restrain the growth of ENTROPY or reduce it in a VolumeMore Particles Due to Chemical ReactionMore Particles AddedIn each of the above sets of pictures, there is a change between the left hand side and the right hand side. Explain how the change would increse the number of ways energy can be distributed in the modern way to describe ENTROPY is to say that en-tropy increases with the number of ways energy can be distributed in a AND THE SECOND LAW OF THERMODYNAMICSENTHALPY AND ENTROPYC onsider this experiment: a drop of water is placed in a clean Petrie dish and the cover is put on.

8 What hap-pens and and what are the causes?The system is the Petri dish and its contents. The sur-roundings include the table and the air outside of the Petri the pictures below. each column shows the same state of the system, but from a different perspective. The fi rst column shows just the changes in molecu-lar location. The SECOND column shows changes in energy (temperature) and the third column shows changes in IncreaseTemperature DecreaseEntropy IncreaseEntropy DecreaseTIMETIMED escribe what is happening to the molecules.

9 What do you think will happen later?Why are the gas phase mol-ecules warmer than the liquid phase in the intermediate time. Why do they return to equal temperature?In the energy column, the gas phase molecules return to their original temperature. Why doesn t the same hold true for ENTROPY ? Is ENTROPY con-served?MOLECULESENERGYENTROPY4 ENTROPY AND THE SECOND LAW OF THERMODYNAMICSFUEL TO FUMESTHERMAL ENTROPY5 ENTROPY AND THE SECOND LAW OF THERMODYNAMICSMIXING OF GASESUNLIKELIKESOLUTIONCONFIGURATIONAL ENTROPY6 ENTROPY AND THE SECOND LAW OF THERMODYNAMICS = 144 = 144x143 = 144x143x142 =4 =144!

10 72! = 144x143 = 144x143x142x141 NUMBER OF MOLECULESNUMBER OF STATESMOLECULAR DISSOCIATIONCONFIGURATIONAL ENTROPY : CELLULAR REPRESENTATION7 ENTROPY AND THE SECOND LAW OF THERMODYNAMICS = 1 =72!144!EXPANDING GASCONFIGURATIONAL ENTROPY :COMBINED REPRESENTATIONM oleculeMolecular WeightWater Water Water18 Dinitrogen DioxygenArgonCarbon Dioxide8 ENTROPY AND THE SECOND LAW OF THERMODYNAMICSDISPERSIBLE ENERGYU niverseSurroundingsSystemEnthalpyEntropy HSurroundings = SystemIf SSystem = 0, then SUniverse = SSurroundings = ( H/T)SystemIn this pictorial representation, the system is shown qualitatively with an original enthalpy and ENTROPY .