24 Determine Aron at 25C for C graphite 2H2g CH4g given the

24. Determine Aron at 25°C for C graphite) + 2H2(g) CH4(g) given the following thermochemical reactions. AH393.5 kJ AH-285.8 kJ MP-890.3 kJ C(graphite) + O2(g) CO2(g) CO2(g) +2H20() CHdg) + 202(g) A. +211 kJ

Solution

24. dHo(rxn) for the reaction

multiply the second equation by 2,

add all three equations and cancel common terms,

C(graphite) + O2(g) --> CO2(g)

2H2(g) + O2(g) ---> 2H2O(l)

CO2(g) + 2H2O(l) ---> CH4(g) + 2O2(g)

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C(graphite) + 2H2(g) ----> CH4(g)

dHo(rxn) = -393.5 + (2 x -285.8) + 890.3

               = -74.8 kJ