Thermodynamics Review Sheet - Principles of Chemistry I | CH 301, Study notes of Chemistry

Download Thermodynamics Review Sheet - Principles of Chemistry I | CH 301 and more Study notes Chemistry in PDF only on Docsity! wqE  First Law of thermodynamics: The energy of the universe is constant A system transfer energy through heat and work w = work E = change in system’s internal energy (U ) q = heat ENDOTHERMIC q > 0 heat flowing into the system; EXOTHERMIC q < 0 heat flowing out of the system w > 0 surroundings do work on the system; w < 0 system does work on the surrounding UNITS: E, q, w = Energy (J) 1 L.atm ~101.34 J Common type of work associated with chemical processes is work done by a gas (expansion), or work done to a gas (compression). VPw  P = external pressure TnCq  TmCq or C = Molar Heat Capacity (J/K-mol) C = Specific Heat Capacity (J/K-grams) Constant Volume TCnormqE v  )( Constant Pressure PVEH  H = Enthalpy TCnormqH P  )( State Functions The value of a state function does not depend on how the system arrived at the present state. A change in this function (property) in going from one state to another is independent of the particular pathway RCv 2 3  RCv 2 5  RCv 2 6  Monoatomic Diatomic Polyatomic RCC vp  Ideal Gases Heat Capacity Calorimeters HTCmq waterswatercal  , - Constant Pressure (coffee-cup) surrsys qq  - Constant Volume (bomb calorimeter) 2 SO2(g) + O2(g) ------- 2 SO3(g) wqE  Hqp  nRTVPw  TCTCmq hardwarewaterswatercal  , In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. Hess’s Law Obtain the Enthalpy change (H) by using a calorimeter can be very difficult Standard enthalpy of formation (Hf o): The change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states. Definitions of Standard States -Gas: Pressure of 1 atm -Solution: Concentration of 1 M at an applied pressure of 1 atm -Pure substance (liquid or solid): the pure liquid or solid -Element: the form in which the element exists under conditions of 1 atm and temperature of 25C )tan()( tsreac o fproducts o freaction o HnHnH   1.When a reaction is reversed, the magnitude of H remains the same, but the signs changes 2.When the balanced equation is multiplied by an integer, the H for that reaction must be multiplied by the same integer 3.Elements in their standard states are not included in the H reaction calculations. That is, hof for an element in its standard state = 0 From Bond Energies   formed bonds-broken bonds H From First Law: If a reaction takes place E = q + w Spontaneous change: -A process is spontaneous if it has a tendency to occur without being driven by an external influence; spontaneous need not be fast. -The entropy (S) is a measure of disorder. Low entropy means little disorder; high entropy means great disorder Second Law of Thermodynamics: The entropy (S) of an isolated system increases in the course of any spontaneous change T q S rev - Change in the entropy (at constant Temperature) S = change in the entropy of the system revrev w V V nRTq        1 2ln There is a natural zero of entropy (state of perfect order) Third law of thermodynamics: The entropies of all perfect crystals approach zero as the absolute temperature approaches zero. Boltzmann’s Formula WkS ln k = Boltzmann’s constant = 1.381x10-23 J.K-1 W = number of ways that atoms or molecules can be arranged at the same energy (microstates)        1 2ln V V nRS Isothermal expansion/compression ideal gas I II Changes in Entropy        1 2ln T T nCS Heating increases thermal disorder.        1 2ln V V nRS Entropy also increases when a given amount of matter spreads into a greater volume or is mixed with another substance b vap vap T H S   f fus fus T H S   So diamond, C > So lead, Pb (heavier atoms have more disorder than lighter atoms) So nitrogen, N2 > S o hydrogen, H2 So calcium carbonate, CaCO3 > So calcium oxide, CaO (large, complex species have higher entropies than those of smaller, simpler ones Entropy increases as the complexity of the substance increases. Entropies of gases are higher than those of comparable solids and liquids at the same temperature Changes in Entropy that accompanies a chemical reaction   )reactants()products( o m o m o r nSnSS Global changes in Entropy surrtotal SSS  Hqsurr T q S surrsurr  T H S surrsurr   At constant pressure: T H SStotal   At constant Temperature and Pressure: S Ssurr Stot Character > 0 > 0 > 0 spontaneous < 0 < 0 < 0 not spontaneous; reverse change is spontaneous > 0 < 0 spontaneous if S is greater than - Ssurr < 0 > 0 spontaneous if Ssurr is greater than -S A process is spontaneous if it is accompanied by an increase in the total entropy of the system and the surroundings Second Law of Thermodynamics