Ammonia burns in the presence of a copper catalyst to form nitrogen gas. 4 NH3(g) + 3 O2(g) → 2 N2(g) + 6 H2O(g) ΔΗ = -1267 kJ What is the enthalpy change to burn 38.4 g of ammonia?​

-713 kJ

Explanation:

Step 1: Write the balaned thermochemical equation

4 NH₃(g) + 3 O₂(g) → 2 N₂(g) + 6 H₂O(g)  ΔΗ = -1267 kJ

Step 2: Calculate the moles corresponding to 38.4 g of NH₃

The molar mass of NH₃ is 17.03 g/mol.

38.4 g × 1 mol/17.03 g = 2.25 mol

Step 3: Calculate the  enthalpy change to burn 2.25 mol of ammonia

According to the thermochemical equation, 1267 kJ are released per 4 moles of ammonia that react.

2.25 mol × (-1267 kJ/4 mol) = -713 kJ

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