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### 20 Cards in this Set

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 Thermodynamics Transfer of energy from one form to another "In" to system/"Out" of system In: +q Out: -q Physical Thermodynamic Equations (2) (1) E = q + w (2) W = -P*V Compressed Gases ____ Expanding Gases _____ WARM! COOL! Isobaric - Constant P - Area under the boxed curve is work done Isochoric - Constant V - No work is done and the total energy is equal to q. - Piston didn't move! Isothermal - Constant T - Heat is transferred freely between system and the environment - E = 0, q = -w Adiabatic - no heat is transferred between the system and the environment - all energy is work - q = 0 (no heat), so E = w. - Also known as a perfectly insulated system Second Law of Thermodynamics - The important one...two ways to interpret it: - Disorder increases in a spontaneous process - All processes run in direction leading to maximum disorder Entropy ΔS = S(prod) - S(reactants) Increase in disorder is +++ Decrease in disorder is ---- Enthalpy ΔH = H(prod) - H(reactants) - Measure of heat released or absorbed at a constant pressure. Always the same for a rxn. - "Breaking Up Is Hard To Do" - If energy is required, ΔH +++ - If energy is released, ΔH ----- Exothermic - Energy Released - Typically when we form bonds - Products in a lower state of energy than the reactants - NEGATIVE NEGATIVE NEGATIVE ΔH! Endothermic - Energy Needed - Typically when we break bonds - Reactants in a lower energy state than products - POSITIVE ΔH! POSITIVE ΔH! Three Ways We Can Calculate ΔHrxn - ΔHrxn is basically just the enthalpy change of a reaction - Heat of Formation - Hess's Law of Summation - Bond Energy Heat of Formation (ΔHf) - Amount of energy required to make one mol of a compound from its constituent elements in their natural state (where ΔHf = 0) ΔHrxn = (n*Products) - (n*Reactants) Conclusions: (+) ΔHf, making compound from element requires heat (endo) (-) ΔHf, making compound from element gives off heat (exo) What are the Standard State parameters used for Thermodynamics? - 25°C, 298K, 1M - This is called ΔH°. Hess's Law of Summation - Sum of the ΔH in individual steps will equal the overall ΔH. - Notes: if reaction is reversed, sign reversed too, and if multiplied by a constant to balance equation, ΔH must be multiplied too Summation of Bond Enthalpies - ΔH can be viewed as energy stored in chemical bonds - "Breaking Up Is Hard To Do" ΔHrxn = (BDE broken) - (BDE formed) Gibbs Free Energy - Energy available to do useful work in a chemical reaction ΔG = ΔH - TΔS Thermodynamics and Equilibrium ΔG° = -RTln(Keq) ΔG = ΔG° + RTln(Keq)