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The enthalpy of combustion of carbon to form carbon dioxide is −393.5 kJ per mole. What is the heat evolved when 35.2 g of CO₂ is produced from carbon and oxygen gas?

1. +315 kJ
2. +315 J
3. −630 kJ
4. −315 kJ

Correct answer: −315 kJ

Solution

The enthalpy of combustion indicates that for every mole of CO₂ produced, 393.5 kJ of heat is released. Since 35.2 g of CO₂ corresponds to 0.8 moles, the total heat evolved is 0.8 moles multiplied by -393.5 kJ/mole, resulting in -315 kJ.

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