CHEM 102Exam 1 Study GuideEntropy + Free Energy1. Reviewa. Enthalpyi. Heat content of a substance at constant pressure ii. Delta H = Hfinal –H initialiii. Delta H > 0 is endothermiciv. Delta H < 0 is exothermicv. Plan1. Find moles of substance (mL to g to mol)2. Use Hrxn to find heatb. State functioni. Quantity determined by state of system1. Change in state depend on initial and final onlya. Pressure is P and Delta Pb. Temperature is T and Delta tc. Volume is V and Delta Vd. Ethalpy is H and delta H2. Lawsa. First lawi. Total energy in universe is constant ii. System under study +surroundings=universe2. Actual chapter 19 stufa. Spontaneous reactioni. Occurs with forward direction without interventionii. Delta H alone does not determine if its spontaneousiii. Also needs the change in the freedom of motion of particles1. Every atom has quantized electronic energyb. Entropyi. Thermodynamic state, AKA disorderii. S=k ln W1. K is 1.381e-23 j/k2. W is microstatea. Vibrationalb. Rotationalc. translationaliii. As W increases, entropy increases1. Lower entropy (fewer microstates, more order) – higher entropy (more microstates, more disorder)a. phase changeb. dissolving saltsc. chemical changed. molecular sizee. temperaturef. volumeiv. S298 is absolute standard molar entropyc. 3rd law of thermodynamics1. Entropy of a pure,perfect crystalline substance is 0 at absolute 0 Kii. Sign convention1. If delta positive, entropy increases2. If delta negative, entropy decreasesd. 2nd law of thermodynamics1. In any spontaneous reaction, the entropy of the universe increases2. Delta S Universe = Delta S system + Delta S Surrounding a. Systemi. nSproducts - nSreactantsb. Surroundingsi. –H system/T(K)ii. Plan1. Calculate S System2. Calculate S Surrounding from H system3. If S universe > 0, reaction is spontaneouse. Gibbs Free Energy i. The amount of energy available for a system to do useful workii. Change1. Maximum amount of useful work that can be done by a reaction at constant T and P2. Gf298a. Standard molar free energy of formation at 25 Ciii. Grxn=delta G system1. G < 0 spontaneous forward2. G > 0 non spontaneous3. G = 0 at equilibriuma. G rxn= sum products – sum reactantsi. Delta H –T Delta Sii. (Change in heat at P)-(always positive T)(Change in amount of disorder)= (indicator of spontaneity) 4. At boiling poit, liquid + gas phase are at equilibrium a. G = 0b.