Question

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N2H4(g) + H2(g) 2 NH3(g) H1 = –1876 kJ

3 H2(g) + N2(g) 2 NH3(g) H2 = –922 kJ

The H f for the formation of hydrazine: 2 H2(g) + N2(g) N2H4(g) will be_____kJ/mol.

Answer 1

Reverse equation 1 and add to equation 2. That will give you the equation desired at the end. Reverse the sign for delta H when the equation is reversed.