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Reacting 0.0500 mol of HCl with 0.0500 mol of NaOH produces 2.9 kJ of heat. What is the enthalpy change per mole of acid?
A-58 kJ
B-2.9 kJ
C+58 kJ
D-145 kJ
Answer & Solution
Correct answer: A. -58 kJ
1. Heat was produced, so the heat for the reaction is negative: minus 2.9 kJ.
2. That amount of heat came from 0.0500 mol of HCl reacting.
3. Form the conversion factor: minus 2.9 kJ per 0.0500 mol HCl.
4. Multiply by 1 mol HCl to get the per-mole value.
5. Minus 2.9 divided by 0.0500 gives minus 58 kJ per mole.
6. Since the balanced equation shows 1 mol of HCl, the thermochemical equation carries minus 58 kJ.
7. Reporting plus 58 kJ would claim the neutralization absorbs heat, contradicting the temperature rise.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.3 Enthalpy_
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