TitrationsTitrations are done to determine the unknown concentrations of unknown acids.It is based of off determining how much known acid or base is needed to reach the equivalence point of the unknown liquid and at what pH the equivalence point exists.The equivalence point is the middle point of the fastest changing pH area. Usually a color indicator is used to help find the equivalence point as well as a pH indicator.
Solubility EquilibriaAdding an ionic solid to water It will be in equilibrium so long as some solid exists in solutionMg(OH)2(s)<-> Mg2+(aq) + 2 OH-(aq) Ksp= [Mg2+][OH-]2 This is the solubility product constant for the above equation Note, the solid is not part of the equation
Predicting precipitationFor Mg(OH)2(s)<-> Mg2+(aq) + 2 OH-(aq) If Q= [Mg2+][OH-]2 < Ksp then the there will be no precipitate. If Q > Ksp then the there will be a precipitate. Note, if Q was < Ksp then only Mg2+(aq) or OH-(aq) would need to be added to cause precipitation.
ThermodynamicsIs the flow of energy1st law of thermodynamics The total energy of the universe is constant, energy can not be created nor destroyed If you decrease the energy in the system, then you increase the energy of the surrounding If you increase the energy in the system, then you decrease the energy of the surrounding U = internal energy = all potential energy + all kinetic energy dU universe = dU system + dU surroundings dU system = - dU surroundings
Thermodynamics 2: heat and workdU system = Heat (q) + Work (w) q= Heat = energy flow from the change in temperature w= Work = energy flow from movement against a forceClosed system- do not allow matter in or out of the systemq<0 – heat flows out of the systemq>0 – heat flows into the systemw<0 – the system does work on the surroundingw>0 – the surrounding does work on the system
Thermodynamics 3: enthalpyThe most common work in chemical systems w= -P dV Work= - Pressure * change in Volume dU system = q – P * dV dH (enthalpy) = dU + d(PV) dH = dU + P*dH @ constant P Plugging in “dU system = q – P * dV” you get: dH = q - P*dH + P*dH = q @ constant P dH = q @ constant P
2nd law of thermodynamicsAll spontaneous processes increase the entropy of the universe dS (entropy) > 0 for spontaneous processesEntropy is a measure of the dispersive-ness of energy A larger value of entropy is a more dispersed energy
Guessing thermodynamicsC6H12O6(s) -> 2 C2H3OH(s) + 2 CO2(g) dH>0 because we are breaking more bonds then we are forming dS>0 because there are more moles on the rightH2O(s) -> H2O(l) dS>0 because liquid is more dispersible than solidH2O(l) -> H2O(g) dS>0 because gas is more dispersible than liquid
Entropy guessing rulesIncrease Entropy Breaking bonds without making new ones Change to a favored phase More moles on the product side
EntropydS universe = (dS system + dS surroundings) > 0dS surroundings = -q / TdS system - q / T > 0 At constant P, q=dH so: dS - dH / T > 0 systemFor phase changes: dS system - dH / T is approximately 0, so: dS system = dH / T
Calculating entropyaA + bB -> cC + dD dS reaction = c*SCo + d*SDo – a*SAo – b*S Bo SAo is the standard entropy of A
Gibbs free energy G = free energy dG = dH – TdS @ constant P and T dG < 0 for a spontaneous process Reactions that are dG>0 won’t happen, but their reverse reaction will Reactions that are dG=0 will have nothing happen because the system is at equilibrium The free energy and the equilibrium constant are related: dGo= - RT ln K dGo is the dG at standard temperature and pressure R is the gas law constant, R=8.314 J/(K*mol) T is the temperature ln K is the natural logarithm of the equilibrium constant
Gibbs free energydG = dH – T*dS @ constant P and TdHo dSo dGo>0, endothermic >0, increase in energy (+)-T(+), more negative at higher temperatures<0, exothermic <0, decrease in energy (-)-T(-), more negative at lower temperatures>0, endothermic <0, decrease in energy (+)-T(-), always positive, never spontaneous<0, exothermic >0, increase in energy (-)-T(+), always negative, always spontaneousAt low T: dG is approximately= dHAt high T: dG is approximately= – T*dS