We can use Hess's law to calculate enthalpy changes that
cannot be measured. One such reaction is the conversion of
methane to ethane:
2 CH41g2 ¡C2H61g2 + H21g2
Calculate the H° for this reaction using the following thermochemical
CH41g2 + 2 O21g2¡CO21g2 + 2 H2O1l2 H° = -890.3 kJ
2 H21g2 + O21g2¡2 H2O1l2 H ° = -571.6 kJ
2 C2H61g2 + 7 O21g2¡4 CO21g2 + 6 H2O1l2 H° = -3120.8 kJ
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