Final answer:
Approximately -1710.54 kJ of heat is transferred when 24.9 g of ammonia reacts with excess oxygen, based on the enthalpy change of the given reaction and the molar mass of ammonia.
Step-by-step explanation:
To determine the amount of heat transferred during the reaction of ammonia with excess oxygen, we use the given enthalpy change for the reaction (ΔH). The provided reaction is NH3 + O2 -> NO + H2O with ΔH = -1170 kJ, which is an exothermic reaction.
This means that 1170 kJ of heat is released when the molar amount of NH3 mentioned in the balanced equation reacts completely.
To calculate the heat transferred when 24.9 g of NH3 reacts, we convert the mass of NH3 to moles using its molar mass (17.03 g/mol).
Number of moles of NH3 = 24.9 g / 17.03 g/mol = 1.462 moles
Since the reaction releases 1170 kJ per mole of NH3, we multiply the moles of NH3 by the enthalpy change to find the heat transferred:
Heat transferred = 1.462 moles × -1170 kJ/mole = -1710.54 kJ
Therefore, when 24.9 grams of NH3 reacts, approximately -1710.54 kJ of heat is released.