CHEM 104 1st Edition Lecture 24 Components of thermochemistry o Will the reaction happen Are reactants converting to products o If so how fast will it go i e kinetics Product favored reactions are spontaneous reactant favored are nonspontaneous o Ex of spontaneous Glycerol l KMnO4 s K2CO3 s Mn2O3 s CO2 g H2O g o Ex of nonspontaneous H2O l 2H2 g O2 g E q w o E internal energy q energy transferred as heat w energy transferred as work o Q and w are always positive if heat work are being transferred into the system vice versa o E Efinal Einitial E is negative if energy is lost to the surroundings positive if energy is gained from the surroundings Heat transfer occurs when o There is temperature difference between system surroundings Q mc T o System undergoes phase change o Chemical reaction occurs Ex of heat energy conversion Cheeto O2 CO2 H2O 9 2 Cal cheeto 1000 cal 1 Cal 4 185 J 1 cal 38000 J cheeto Enthalpy change H qp heat transferred into system at constant pressure o E H w w is small for chemical equations so E H How to obtain H for a system o Calorimetry o Calculate from known thermochemical equations Hess s law o Calculate from standard molar enthalpies of formation o Estimate from bond enthalpies Processes can be spontaneous at some temperatures but not at others o Ex melting of water is temperature dependent In a reversible process the system changes so that the system and surroundings can be put back in their original states by the same pathways o Irreversible processes cannot be undone by exactly reversing the change to the system Spontaneous reactions are irreversible
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