MSE 508Dept. of Materials Science & Engineering Solid State ThermodynamicsSpring 2011/Bill Knowlton Problem Set 3To determine the ΔHrxnfor the reaction in which a compound is formed, Hess' law can be used: productreactantrxniiiiiiHnHnHFor more complicated reactions in which two compounds react to form another more complicated compound, the reaction is divided into formation "1/2" reactions. For instance, take the more complicated reaction: MAO2+MBO2=MAMBO4This reaction can be separated into the following formation "1/2" reactions: -(MA+ O2= MAO2) -ΔHrxn,1-(MB+O2=MBO2) -ΔHrxn,2MA+MB+2O2= MAMBO4ΔHrxn,3_____________________ MAO2+MBO2=MAMBO4Note that all three reactions are written as formation reactions and "add" together to form the overall reaction. Also note that the first two reactions are written in the opposite direction as what is shown for the overall reaction; this is why they are shown with a negative signs. The overall change in the enthalpy of reaction can be written as the sum of the enthalpy
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