Given the thermochemical equations below find the deltaHrxn

Given the thermochemical equations below, find the deltaHrxn of the formation of mercury(II)oxide, as catalyzed by water electrolysis: Hg(l) + H2O yields HgO(s) +H2 (g); 2H2(g) + O2 yields 2H2O (l) delta H= -286 kJ; 2HgO(s) yields 2Hg(l) + O2(g) delta H= 90.7 kJ

Solution

Hg(l) + H2O --------> HgO(s) +H2 (g);

2H2(g) + O2 ---------> 2H2O (l)    delta H= -286 kJ; -------------> 1

2HgO(s) ------------> 2Hg(l) + O2(g) delta H= 90.7 kJ   ------------> 2

first reverse the equation 2 . and divide by 2

Hg (l) + 1/2 O2 (g)    --------------> HgO (s)     delta H = - 45.35 kJ

reverse the equation 1 and divide by 2

H2O (l)   --------------> H2 (g) + 1/2 O2 (g) delta H = 143 kJ

Now add both the equations :

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Hg(l) + H2O (l) --------> HgO(s) +H2 (g);    delta H = 97.65 kJ