Bond enthalpies: H-H 436, Cl-Cl 243, H-Cl 432 kJ mol-1. What is the enthalpy change for H2 + Cl2 -> 2HCl?
Answer and explanation
Correct answer: B. -185 kJ mol-1
- Step 1: Bonds broken: . Step 2. Bonds made: . Step 3. . Answer: -185 kJ mol-1. Why not the others: +185 reverses the sign; -1111 adds all three bond enthalpies; -92.5 is the figure per mole of HCl, not per equation.
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