Answer:
-191 kJ
Step-by-step explanation:
The given reaction is:
N₂(g) + 3H₂(g) → 2NH₃(g) ΔH = -76.4 kJ/mol
From the balanced equation, we can see that the stoichiometric ratio between hydrogen (H₂) and ammonia (NH₃) is 3:2. This means that 3 moles of hydrogen react to produce 2 moles of ammonia.
To determine the heat energy when 5.0 g of hydrogen (H₂) burns, we need to follow these steps:
Step 1: Calculate the moles of hydrogen (H₂)
Using the molar mass of hydrogen (H₂), which is 2 g/mol, we can calculate the moles of hydrogen (H₂) in 5.0 g of hydrogen:
Moles of H₂ = Mass of H₂ / Molar mass of H₂
Moles of H₂ = 5.0 g / 2 g/mol
Moles of H₂ = 2.5 mol
Step 2: Use the stoichiometry of the reaction
Based on the stoichiometry of the reaction, we know that 3 moles of hydrogen (H₂) react to produce 2 moles of ammonia (NH₃), and the enthalpy change (ΔH) is -76.4 kJ/mol.
Step 3: Calculate the heat energy
The heat energy for 2.5 moles of hydrogen (H₂) can be calculated using the given enthalpy change (ΔH) and the stoichiometry of the reaction:
Heat energy = Moles of H₂ x ΔH
Heat energy = 2.5 mol x -76.4 kJ/mol
Heat energy = -191 kJ (rounded to three significant figures)
So, the heat energy when 5.0 g of hydrogen (H₂) burns is -191 kJ (rounded to three significant figures), and the negative sign indicates that the reaction is exothermic, releasing heat.