The reaction of cyanamide, NH CN with oxygen was run in a bomb calorimeter and ∆U was found to be -7 — Thermodynamics and Thermochemistry Chemistry Question
Question
The reaction of cyanamide, NH CN with oxygen was run in a bomb calorimeter and ∆U was found to be -742.14 kJ mol . The magnitude of ∆H for the reaction is ________ kJ. (Rounded off to the nearest integer) [Assume ideal gases and R = 8.314 J mol K ] 2 (s) -1 298 -1 -1
💡 Solution & Explanation
**Step 1: Write the balanced equation for cyanamide combustion** NH₂CN(s) + 3/2 O₂(g) → N₂(g) + CO₂(g) + H₂O(l) **Step 2: Identify the relationship between ∆H and ∆U** ∆H = ∆U + ∆(nRT) = ∆U + ∆n_gas·RT where ∆n_gas = moles of gaseous products − moles of gaseous reactants **Step 3: Calculate ∆n_gas** - Gaseous products: N₂(g) + CO₂(g) = 2 moles - Gaseous reactants: 3/2 O₂(g) = 1.5 moles - ∆n_gas = 2 − 1.5 = 0.5 mol **Step 4: Calculate ∆(nRT)** ∆(nRT) = 0.5 mol × 8.314 J/(mol·K) × 298 K ∆(nRT) = 1,240.79 J = 1.24 kJ **Step 5: Calculate ∆H** ∆H = ∆U + ∆(nRT) ∆H = −742.14 + 1.24 ∆H = −740.90 kJ ≈ −741.00 kJ **Step 6: Report the magnitude** The magnitude of ∆H = |−741.00| = 741.00 kJ Therefore, the answer is 741.00.