A Levels Chemistry (9701)•9701/11/M/J/21
Explanation
Energy profile indicating endothermic reaction
Steps:
- Identify reaction type from energy profile: products higher than reactants signals endothermic.
- Evaluate A: CaCO₃ decomposition requires heat input, endothermic with ΔH > 0.
- Evaluate B: H₂O₂ decomposition releases heat, exothermic with ΔH < 0.
- Evaluate C: Cl⁻ ionization from aqueous to gas is endothermic but lacks gas evolution matching diagram.
- Note D incomplete, cannot assess.
Why A is correct:
- Matches endothermic profile per Hess's law, where ΔH equals enthalpy change for thermal decomposition.
Why the others are wrong:
- B: Exothermic, profile would show products lower than reactants.
- C: Endothermic but electrochemical, not thermal decomposition with CO₂ gas.
- D: Insufficient information provided.
Final answer: A
Topic: Chemical energetics
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