When `12.0g` of `C` reacted with oxygen to form `CO` and `CO_(2)` at `25^(@)C` at constant pressure, `313.8 kJ` of heat was released and no carbon remained. Calculate the mass of oxygen which reacted.
`Delta_(f)H^(Theta) (CO,g) =- 110.5 kJ mol^(-1)` and
`Delta_(r)H^(Theta) (CO_(2),g) =- 393.5 kJ mol^(-1)`

Explanation

To solve the problem, we need to calculate the mass of oxygen that reacted when 12.0 g of carbon was burned to form carbon monoxide (CO) and carbon dioxide (CO2) while releasing 313.8 kJ of heat. We will use the given enthalpy values for CO and CO2 to set up our equations.

### Step-by-Step Solution:

1. **Calculate the number of moles of carbon (C) reacted:**
\[ \text{Molar mass of C} = 12 \, \text{g/mol} \]
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