Question

4. Use the tabulated values of enthalpy of formation in Appendix 4 of your text to calculate the enthalpy change of the following reactions: (a) Hydrazine [N2 H, (0)] and gaseous dinitrogen tetroxide form a self-igniting (hypergolic) mixture that has been used as a rocket propellant. The reaction products are nitrogen gas and water vapor. (b) The thermal decomposition of mercury(II) oxide to produce liquid mercury and oxy- gen gas. (c) Inside a blast furnace, excess silicon dioxide is removed from the melt by reacting it with calcium oxide, forming solid calcium silicate, CaSiO3

Answer 1

Compound enthalpy of formation I (KJ/mol) Na Hu (1) 50.63 N₂O4 (9) 9.16 0 - 241.82 - 90.83 N(g) - H₂O (9) Hgo - .Hg (1) - 02.09 SiO2 - CaO Casio I c) -910.86 - 635.5 - 1630

reactants aj a N, Hy (l) + N, 04 (9) >3N, 19) +*4.019) Ato reaction = 4H of products - Alt of - ( 3 44 N2 (9) + 4 AH, 42019)) - (2 4H; #¢CI) + 4H : N, 0409)) = ( 3 x0) + 4(-241.2)) = (2x50:62) + (9.16)) = -1077.7 kJ/mol Answer: -1077.7 kJ/mol.

5 ; =(avat Hy ) + 44; 9.09)–(ex ay". Hgo) 2HgO A > 2Hg (M) + 2 (9) AH," = ((2x0) + (0)) - (2x -90.83) AH = +181.86 kJ/mol Answer: +181.66 kJ/mol.

c) siq (s) + CaO (6) Casio (s) 4H = (Ahf, Casio (6)) - (AH, Siggs) + - AH CAO(0) = -1630- (-910.86 +6=135.5)) = -83.64 KJ/mol Answer: -83.64 kJ/mol.