BONUS: A grad student made the news for all the WRONG reasons a few years ago wh
ID: 511022 • Letter: B
Question
BONUS: A grad student made the news for all the WRONG reasons a few years ago when he synthesized "nickel hydrazine perchlorate" compound (but didn't give any more detailed information) on a scale 1000 times larger than what his lab advisor told him to make (10g instead of 0.010g) and ground it with a mortar and pestle (when the compound is explosive and shock-sensitive) and doused it with hexane (flammable solvent). The student lost a few fingers when the compound exploded. The likely formula for the compound is Ni(N_2H_4)_2(ClO_4)_2, where the hydrazine is a neutral ligand and the nickel is +2. If 10g of this compound reacted completely into its component elements, how many liters of gas would be produced at 298K and 1 atm? If you imagined the hydrazine decomposition and the nickel/perchlorate decomposition as separate reactions, how much energy would be given off? (The heats of formation for hydrazine and nickel (II) are in your text; I had to estimate the heat for formation for perchlorate but assume it to be approximately 200kJ/mol)Explanation / Answer
Ni(N2H4)2(ClO4)2 <==> Ni^2+ + 2N2 + Cl2 + 4O2 + 4H2
If 1 mole of the compound decomposes, 2 moles of N2, 1 mol of Cl2, 4 mol of O2 and 4 mol of H2 will be produced. total number of moles of gas = 11 moles
moles of the Ni(N2H4)2(ClO4)2 = 10gm/ 321.68 gm/mol = 0.031 mol
moles of gas formed = 11 * 0.031 mol = 0.342 mol
At STP 1 mol of gas = 22.4 L
So, 0.342 mol = 0.342 * 22.4L = 7.66 L
So, 7.66L gas will be produced.
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heat of formation of Ni^2+ = -54.0 kJ/mol
heat of formation of NH2NH2 =50.63 kJ/mol
heat of formation of ClO4^- =200kJ/mol
1 mol of Ni(N2H4)2(ClO4)2 contains 1 mol Ni 2 moles of N2H4 and 2 moles of perchlorate
Amount of energy released during the decomposition
= 1* -54kJ/mol + 2*50.63 kJ/mol + 2* 200kJ/mol = 447.26 kJ
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