Thermodynamics Unit

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Thermodynamics in AP Chemistry
Rachel Todd
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Rachel Todd
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Zusammenfassung der Ressource

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