ThermodynamicsEnergy StatesPowerPoint PresentationSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12ThermodynamicsThermodynamicsa a system:system:Some portion of the universe that you wish to studySome portion of the universe that you wish to studythe the surroundings:surroundings:The adjacent part of the universe outside the systemThe adjacent part of the universe outside the systemChangesChanges in a system are associated with the in a system are associated with the transfer of energytransfer of energyNatural systems tend toward states of minimum energyNatural systems tend toward states of minimum energyEnergy StatesEnergy StatesUnstable:Unstable: falling or rollingfalling or rollingStable:Stable: at rest in lowest energy stateat rest in lowest energy stateMetastable:Metastable: in low-energy perchin low-energy perchFigure 5-1. Stability states. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.A review of basic thermodynamics: A refresherA review of basic thermodynamics: A refresherThe ball representsThe ball representsmass exchangemass exchangeThe arrow representsThe arrow representsenergy exchangeenergy exchangeThe First Law of ThermodynamicsThe First Law of Thermodynamics• Heat and work are equivalent• Energy is conserved in any transformation• The change of energy of a system is independent of the path takenEnergy can be neither created nor detroyedE = q - w or dE = dq - dwE = internal energyq = heatw = workdE = dq - P dVP = pressureV = volumeEnthalpyEnthalpydE = dq - P dVH = E + PVdH = dqH = enthalpyThe change in the enthalpy of a system (H) during a reversiblechange in state at constant pressure is equal to the heat absorbedby the system during that change in state.The enthalpy of formation of compounds and their ions and molecules in aqueous solution is the heat absorbed or given off bychemical reactions in which the compounds, ions, and moleculesform from the elements in the standard state (25°C, 1 atm)Heats of ReactionHeats of ReactionH =  nH (products) -  nH (reactants)n = molar coefficient of each reactant/productWhen H is positive, the reaction is endothermic (heat flowsfrom the surroundings to the system); When H is negative, the reaction is exothermic (heat flows from the system to the surroundingsHeats of ReactionHeats of ReactionH =  nH (products) -  nH (reactants)For example, evaporation: H2O(l) H2O(g)H = H(H2O(g)) - H(H2O(l)) H = (-57.80) - (-68.32) = 10.52 kcalThe reaction is endothermic (i.e., sweating is a mechanism for cooling the body)Heat CapacityHeat CapacityWhen heat is added to a solid, liquid, or gas, the temperatureof the substance increases: dq = C dTdq = dHdH = C dT, at constant pressure (important in geochemistry)C = heat capacityT = temperatureHeat capacities vary with temperature…The Second Law of ThermodynamicsThe Second Law of Thermodynamics• It is impossible to construct a machine that is able to convey heat by a cyclical process from one reservoir at a lower temperature to another at a higher temperature unless outside work is done (i.e, air conditioning is never free)• Heat cannot be entirely extracted from a body and turned into work (i.e., an engine can never run 100% efficiently) — a certain fractionof the enthalpy of a system is consumed by an increase in entropy• Every system left to itself will, on average, change toward a condition of maximum randomness — entropy of a system increases spontaneously and energy must be spent to reverse this tendencyThe entropy of the universe always increasesor“You can’t shovel manure into the rear end of a horse and expect to get hay out of its mouth”S =  nS (products) -  nS (reactants)For example: H2O(l) H2O(g)S = S(H2O(l)) - S(H2O(g)) S = 45.10 - 16.71 = 28.39 cal/degWhen S is positive, entropy of the system increases with the change of state;When S is negative, entropy decreases EntropyEntropyThe ratio of heat gained or lost to temperature will alwaysbe the same, regardless of path, for a reversible reactiondE = T dS - P dVWhen dE = 0, T dS = P dVdS = dq/T = P dV/TThe fundamental equation of thermodynamicsThe fundamental equation of thermodynamicsdS = dq/T — reversible processdS > dq/T — irreversible processdPdTSVLook