Answer
-583 kJ/mol
Work Step by Step
Compute moles of N2H2:
6.50 g / 30.0298 g/mol = 0.21645 mol
Determine enthalpy per mol:
126.2 kJ / 0.21645 mol = 583 kJ/mol (to three sig figs)
Since the reaction is exothermic, the final answer is:
-583 kJ/mol