Lecture 43

# Lecture 43 - Exam Four TONIGHT 7 9 pm You may not leave...

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Exam Four! TONIGHT 7 - 9 pm You may not leave before, or start after, 7:45 pm. You will need: non-programmable calculator UT student ID card several #2 pencils and an eraser empty bladder Don’t Forget room change Surname starting with A–L? Go to GEA 105 Surname starting with M–Z? Go to GAR 0.102 Surnames M–Z GAR 0.102 Surnames A–L GEA 105 Questions are randomized At start of time, scan through so there are no surprises. Mark the calculations, the easy ones, the ones you will have to think about. Note point values. Do the easy ones first. Put off the hardest ones til last. Keep track of time. Make notes on the concept questions. Check and double check that you have correctly entered each answer on the scantron sheet, along with your EID, and your exam version #. Keep your copy of your exam 1 2 3

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Don’t forget some constants and conversion factors are on the back of the scantron sheet. I’m just going to use last years formula sheet. It’s been online since the weekend. A copy will be supplied with your exam tonight. Exam Breakdown 25% : Heat and Work 50% : Thermochemistry (calculations for specific chemical reactions of H, S, G) 25% : Entropy and Free energy Internal energy change is either heat or work: Δ E = q + w Heat Capacities: q = C Δ T; q = s m Δ T q = C m n Δ T Constant P calorimetry Δ H rxn = q rxn = – (m soln s soln Δ T + C cal Δ T) Constant V calorimetry q rxn = – (m water s water Δ T + C cal Δ T) Hess’s law: Δ rxn = Δ H a ˚ + Δ H b ˚ + Δ H c ˚ + ... Given heats of formation: Δ rxn = Σ Δ H f ˚(prod) – Σ Δ H f ˚(react); Δ rxn = Σ Δ G f ˚(prod) – Σ Δ G f ˚(react) Given absolute entropies: Δ rxn = Σ S f ˚(prod) – Σ S f ˚(react) For elements in their standard form: Δ f = Δ f = 0 Given bond energies (gas only): Δ rxn = Σ BE (react) – Σ BE (prod) Work: w = –P Δ V = – Δ nRT; Δ E = q + w = q – P Δ V = q – Δ nRT Enthalpy: H = E + PV; Δ H = Δ E + Δ (PV) = Δ E + Δ n gas RT Entropy: Δ S = –q/T; Δ S = – Δ H/T Gibbs Free Energy: G = H – PV; Δ G = Δ H –T Δ S The study of energy changes in a system We can talk about whether or not a reaction is spontaneous, and what the energy changes are during a reaction. We cannot talk about the reaction rate (how fast a reaction occurs) Definitions System, surroundings, universe Open, closed, isolated State functions The change in a state function is independent of pathway Δ X = X final – X initial Thermodynamics 4 5 6
Two types of energy: Kinetic (energy of motion) and Potential (energy due to position or composition) Two ways for energy to flow in or out of a system: Heat and Work First Law of Thermodynamics: The energy of the universe is conserved.

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