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The heat of combustion of carbon to CO2 is -393.5 kJ/mol. The heat released upon formation of 35.2 g of CO2 from carbon and oxygen gas is:

1. -315 kJ
2. +315 kJ
3. -630 kJ
4. +3.15 kJ

Correct answer: -315 kJ

Solution

The molar mass of CO2 is 44 g/mol. For 35.2 g of CO2, the number of moles is 35.2/44 = 0.8 mol. The heat released is 0.8 × (-393.5) = -315 kJ.

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