Chem 1061 1st Edition Lecture 15 Outline of Last Lecture I Units of Energy II Enthalpy III Exothermic and Endothermic Processes IV Calorimetry V Specific Heat Capacity VI Molar Heat Capacity VII Calorimetry Outline of Current 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 Current Lecture Determining H of a Reaction Coffee Cup Calorimeter calculation T initial 22 4 degree C T final 23 0 degree C V 85 0 g H2O Reaction flash bulb Zr Equation Zr s O2 g ZrO2 s H Zr 0 0223 g O2 In excess q lost q gain 0 q rxn q H2O 0 H q rxn mol ZrO2 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 0 0223 g Zr x 1mol Zr 91 22g Zr x 1mol ZrO2 1mol Zr 0 000244 mol ZrO2 q rxn c H2O x m H2O x T 0 q rxn 4 184 J g C x 85 0 g x 23 0 C 22 4 C 0 q rxn 213 38 J q rxn mol ZrO2 213 38J 0 000244 mol 8 75 x 10 5 J mol 875 kJ Heat lost to both water and calorimeter Calorimeter is constant c cal J K J C No mass component because you cannot have one half of a calorimeter or one and one half of one q gain q H2O q cal q cal c cal x T Bomb calorimeter way to do constant volume calorimetry used for combustion reactions Stoichiometry of Thermochemical Equations Reaction H on appropriate side H endothermic heat in heat is reactant H exothermic heat out heat is product 1 Reverse reaction reverse the sign on H H2O l H2 g 1 2 O2 g H 286 K J H2 g O2 g H2O l H 286 K J 2 Change magnitude of coefficient then the magnitude of H is changed PROPORTIONALLY Balancing Coefficients H specified for particular amount often 1 mol H f use fractional coefficients as necessary C s 1 2 O2 g CO g H 110 5 kJ Thermochemical Equations 110 5 is thermochemically equivalent to 1 mol C s mol O2 g 1 mol CO g Ex 2P s 2Br2 l 2PBr3 g H 243kJ What is the enthalpy when 2 63g P s reacts with excess Br2 l 2 63 g P s x 1 mol P s 30 97 g P s x 243 kJ 2 mol P s 10 3 kJ
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