mass of nitrogen was produced

Question

Nitromethane, CH₃NO₂, can be used as a fuel. When the liquid is burned, the (unbalanced) reaction is mainly

CH₃NO₂ (l) + O₂ (g) à CO₂ (g) + N₂ (g) + H₂O (g)

a.) The standard enthalpy change of reaction (ΔH^o_rxn) for the balanced reaction (with lowest whole- number coefficients) is -1288.5 kJ. Calculate the ΔH^o_f for nitromethane.

b.) A 15.0 L flask containing a sample of nitromethane is filled with O₂ and the flask is heated to 100°C. At this temperature, and after the reaction is complete, the total pressure of all the gases inside the flask is 950 torr. If the mole fraction of nitrogen (X_nitrogen) is 0.134 after the reaction is complete, what mass of nitrogen was produced?

Answer 1

4CH₃NO₂(l) + 7O₂(g) ==> 4CO₂(g) + 2N₂(g) + 6H₂O(g) ... balanced equation ∆Hº_rxn = -1288.5 kJ

∆Hº_rxn = -1288.5 kJ = ∆Hºf products - ∆Hºf reactants

You will have to look up the ∆Hºf of each reactant and product (it will be zero of N2 and O2) and multiply by the coefficients in the balanced equation and then solve for ∆Hºf of CH₃NO₂.

PV = nRT

(950 torr)(15.0 L) = n(62.36 Ltorr/Kmol)(373K)

n = 0.612 moles of gas

0.612 moles of gas x 0.134 = 0.082 moles N₂ x 28 g/mol = 2.3 g N₂