According to the balanced eqation and heat of reaction
shown:
Heat associated with the reaction of 4 moles of NH3 (4 x 17 g =
68 g) with oxygen = -906 kJ
So, the heat associated with the reaction 1 g of NH3 with oxygen
= -906/68 kJ
So, the heat associated with the reaction 284 g of NH3 with
oxygen = -906 x 284/68 kJ
                                                                                                Â
= 3783.88 kJ
