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In that gummy bear reaction, 43.7 kJ is produced from 0.0587 mol of the limiting KClO3. What is the enthalpy change for the equation as written?
A-43.7 kJ
B-745 kJ
C-5960 kJ
D+5960 kJ
Answer & Solution
Correct answer: C. -5960 kJ
1. Heat was produced, so the value carried forward is minus 43.7 kJ.
2. That heat came from 0.0587 mol of the limiting reactant, KClO3.
3. The conversion factor is minus 43.7 kJ per 0.0587 mol KClO3.
4. The balanced equation is written for 8 mol of KClO3.
5. Multiply: 8 times minus 43.7 divided by 0.0587.
6. Minus 43.7 divided by 0.0587 is minus 744.5 kJ per mole.
7. Multiplying that by 8 gives about minus 5960 kJ for the equation as written.
8. Stopping at minus 745 kJ reports the per-mole figure and forgets the coefficient of 8.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.3 Enthalpy_
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