Thermodynamics Unit

Thermodynamics Unit

1. Energy

   • Can be TRANSFERED
     • HEAT
       • Change in system's energy ΔE = q + W
         • System
           • ex) a solution of HCL and another of NaOH were mixed together in a beaker with a stir rod
             • Solution Chem: only the HCl and NaOH melecules (H+, OH-)
         • Surrounds
           • EVERYTHING ELSE
         • What Causes Chemical Rxns?
           • Free Energy ("nature of reactants")
             • ΔG = ΔH - TΔS
               • ΔG: the max amount of energy that can be used to do work
               • ΔH: energy transferred as heat
               • TΔS: energy used to create disorder
               • - : thermodynamically favoured (spontaneous)
               • + : NOT thermodynamically favoured
               • Calculate
                 • #1: Calculate ΔH from calorimtry OR Hess's OR ΔHf; then calculate ΔS using entropy values; and then plug in to find ΔG at a certain temp
                 • #2: Calculate ΔG using ΔGfº values
                   • (ΔG = ΣnΔGº (products)−ΣnΔGº (reactants))
           • Entropy Δs: measure of disorder *more random wanted*
             • 2nd law: Entropy of Universe is always increasing
             • ΔS = S(products) - S(reactants)
               • ΔSrxn = ΣnSº(products) - ΣnSº(reactants)
               • Positive value is WANTED
           • Enthalpy
             • 1st Law of Thermodynamics: cannot be created or destroyed
               • EXO
                 • ΔH = q = -
               • ENDO
                 • ΔH = q = +
             • can be calculated 4 ways
               • #3 Hess's Law
                 • if a rxn is carried in 1 or several steps, the overall change in enthalpy is equal to the sum of the enthalpy changes for each step
               • #2 Calorimeter
                 • Heat transfer cannot be directly measured
                   • Heat Capacity [kJ/K (or Cº)]
                     • Specific heat capacity: amount of heat needed to raise the temperature of 1 kg of a substance by 1 k [kJ/kg•K (or Cº)]
                       • ΔH rxn vs Δq rxn [ΔH = Δq/n]
                         • total amount of heat lost or gained by a rxn
                         • Using stoichiometry
               • #1 Bond of Enthalpies
                 • Break bonds NEED energy
                   • For the image: A + B need energy to break up; C + D release energy when formed
                 • Form bonds REALEASE energy
                   • ΔH = ΣnBE - ΣnBE
                     • Σ = sum
                     • n = # of moles
                     • BE = bond energy *from exp't* values must be given
               • #4 Enthalpy of Formation
                 • An arbitrary value that indicates how much heat would be lost/gained from experimental states
                   • ΔHº rxn=ΣnΔHºf (products)−ΣnΔHºf (Reactants)
                     • n: mol
                     • Most "Hº"'s will be given
         • q (+): heat transferred IN
           • q (-): heat transferred OUT
         • w (+): work done ON the system
           • w (-): work done BY the system
         • ΔE is change in PE and KE of particles in a system
     • WORK W = -PΔV
   • PE
   • KE
     • Temperature
       • Conversions
         • C = K - 273
         • C = (5/9)(Fº - 32)
       • a measure of the average KE of particles in a system
         • If KE doubles, the temp doubles as well
   • CANNOT BE CREATED OR DESTROYED

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