Stoichiometric amounts of nitrogen gas and hydrogen gas react in a calorimeter to produce 5.00 g of ammonia gas. The calorimeter temperature rises 0.42°C. The calorimeter and water have a combined heat capacity of 32.16 kJ/K. Calculate the heat of formation of ammonia, $\Delta$H_f^°, in kJ/mol. The formation reaction for ammonia is: 0.5N₂(g) + 1.5H₂(g) $\to$ NH₃(g).

Question

Quizplus · Accepted Answer

The heat absorbed by the calorimeter is calculated using q = CΔT = 32.16 kJ/K * 0.42 K = 13.5072 kJ. Since 5.00 g of NH₃ is produced, we convert this to moles (5.00 g / 17.03 g/mol = 0.2937 mol). The heat of formation per mole is then -13.5072 kJ / 0.2937 mol = -46 kJ/mol.

Stoichiometric Amounts of Nitrogen Gas and Hydrogen Gas React in a Calorimeter