Chem 1061 1st Edition Lecture 16 Outline of Last Lecture II Determining H of a Reaction III Heat lost to both water and Calorimeter a Bomb Calorimeter b Combustion IV Stoichiometry of Thermochemical Equations V Balancing Coefficients VI Thermochemical Equivalence Outline of Current Lecture VII Hess s Law Adding Reactions and Enthalpies VIII Standard Enthalpies of a Reaction a Standard Condition b Heat of Formation Current Lecture Hess s Law Adding Reactions and Enthalpies Find H of a missing reaction if you know the others H only depends on initial and final states doesn t depend on path taken to get there Target Equation NH3 g HCL g NH4Cl s H Given 1 N2 g 3 2H2 g NH3 g H 45 9kJ 2 H2 g Cl g HCl g H 92 3kJ 3 N2 g 2H2 g Cl2 g NH4Cl H 314 4kJ Flip 1 so NH3 is a reactant also flip H sign NH3 g 1 2N2 g 3 2 H2 g H 45 9 Flip 2 so HCl is a reactant also flip H sign HCl g 1 2H2 g Cl2 g 92 3kJ These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute MAKE SURE EQUATIONS MATCH Reactants NH3 g HCl g 1 2N2 g 2H2 g Cl g Products N2 g 3 2H2 g H2 g 1 2Cl2 g NH4Cl s THEY MATCH Add up 1 3 so they balance cancel out to the target Do the same manipulations to H H overall H1 H2 H3 45 9kJ 92 3 kJ 314 4 kJ 176 2 kJ Standard Enthalpies of a Reaction Standard Condition state Gas 1 atm ideal behavior aqueous solutions 1 M pure substances must be in stable form at 1 atm and 25 C Symbol used to show variable has been measured with all substances in their standard forms states H rxn Standard Formation 1 mol of a compound forms from elements in their standard form H f of MgO s Mg s 1 2O2 g MgO s 0 0 601 8kJ Know elements are defined at 0kJ compounds differ from that
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