# chem chapter 18

 The flashcards below were created by user Anonymous on FreezingBlue Flashcards. internal energy U is the sum of the kinetic and potential energies of the particles making up the sustem kinetic energy includes the energy of motion of eleectrons nuclei and molecules potential energy includes chemical bonding of atomsattractions between molecules internal energy is a state function which is a property of a system that depends only on its present state which is completely determined by variables such a s temperature and pressure calculate the change in internal energy deltaU = Uf-Ui two types of echanges of energy heat and work heat the energy that moves into or out of the system because of a temperature difference between the system and its surroundings work the energy exchange that results when a force F moves an object through a distance d; w=df the first law of thermodynamics deltaU = q+wthe change in internal energy of a system equals q+w subscript p indicates process occurs at constant pressure (pressure of the atmosphere) formula for work in an open vessel w=-P(deltaV) relating work and internal energy deltaU = qp +w = qp -P(deltaV) enthalpy the quantity U+PV  all are state functions enthalpy formulas deltaH =Hf -Hi deltaH = (deltaU)=P(deltaV) spontaneous process a physical or chemical change that occurs by itself non spontaneous reactions go in the opposite direction entropy (S) is a thermodynamic quantity that is a measure of how dispersed the energy of a system is among the different possible ways that a system can contain energy units for entropy joules per kelvin state function calculate entropy deltaS=Sf-Si the entropy of a solid is _________ than the entropy of a liquid lowerless movement in moleculesfixed therefore energy is fixed second law of thermodynamics the total entropy of a system and its surroundings always increases for a spontaneous process difference between energy and entropy (energy dispersion) energy can not be created nor destroyedentropy can be created heat flow is also a flow of entropy because it is a dispersal of energy into the flask or outside of it  deltaS = entropy created +q/T the quantity of entropy created during a spontaneous process is positive restated second law of thermodynamics for a spontaneous process at a given temperature T the change in entropy of the system is greater than the heat divided by the absolute temperature q/T under equilibrium conditions n no significant amount of entropy is created ex water and ice at 0 degrees C and vaporization of liquid  DeltaS =q/T (equilibrium process) to determine if a reaction is spontaneous delta S > DeltaH/Tat constant pressure and temperature  also if DeltaH-T(deltaS) is negative then it is spontaneous as written  if it equals zero then it is at equilibrium third law of thermodynamics a substance that is perfectly crystalline at 0 K has an entropy of zero  should have perfect order standard entropy / absolute entropy S0 is the entropy value for the standard state of the species entropy increases when: 1. a reaction in which a molecule is broken into two or more smaller molecules2. a reaction in which there is an increase in moles of gas3. a process in which a solid changes to liquid or a liquid changes to a gas free energy G thermodynamic quantity defined by the equation G=H-TS this quantity gives a direct criterion for spontaneity of reaction values of G negative -- spontaneouspositive -- non spontaneouszero -- equilibrium standard free energy of formation the free energy change that occurs when 1 mol of substance is formed from its elements in their stables states at 1 atm and at a specified temperature (usually 25 degrees C or 298 K) DeltaG0 as a criterion for spontaneity - when it is a large negative number more than -10 KJ the reaction is spontaneous as written and reactants transform almost entirely to products when equilibrium is reached DeltaG0 as a criterion for spontaneity -when it is a large positive number more than 10 KJ the reaction is non spontaneous as written and the reactants do not give significant amounts of products at equilibrium DeltaG0 as a criterion for spontaneity -when it is a small positive or small negative number less than -10 KJ and 10 KJ the reaction gives an equilibrium mixture with significant amounts of both reactants and products spontaneous reactions are used to obtain useful work -- energy that can be used directly to move objects to obtain maximum useful work no entropy is produced wmax=DeltaG free energy the maximum energy available to do useful work thermodynamic equilibrium constant K the equilibrium constant in which the concentrations of gases are expressed in partial pressures in atmospheres whereas the concentration of solutes in liquid solutions are expressed in molarities obtain delta G from the following equation DeltaG=-RTlnK G -- free energyR -- constant 8.3145 T -- temperatureK -- constant H is negative  S is positive G is negative spontaneous at all T H positive  S negative G positive nonspontaneous at all T H negative  S negative  G either positive or negative spontaneous at low T non spontaneous at high T H positive S positive G either positive or negative spontaneous at high Tnon spontaneous at low T AuthorAnonymous ID260606 Card Setchem chapter 18 Descriptionchem Updated2014-02-06T21:21:24Z Show Answers