The heat of combustion of carbon to `CO_(2)` is `-393.5` kJ/mol. The heat released upon formation of 35.2 g of `CO_(2)` from carbon and oxygen gas is

Options

A. `+315` kJ
B. `-31.5` kJ
C. `-315` kJ
D. `+31.5` kJ

Explanation

To find the heat released upon the formation of 35.2 g of CO₂ from carbon and oxygen gas, we can follow these steps:

### Step 1: Determine the molar mass of CO₂
The molar mass of CO₂ can be calculated as follows:
- Carbon (C) has a molar mass of approximately 12.01 g/mol.
- Oxygen (O) has a molar mass of approximately 16.00 g/mol.

Since CO₂ has one carbon atom and two oxygen atoms:
\[ \text{Molar mass of CO₂} = 12.01 \, \text{g/mol} + 2 \times 16.00 \, \text{g/mol} = 12.01 \, \text{g/mol} + 32.00 \, \text{g/mol} = 44.01 \, \text{g/mol} \]

### Step 2: Calculate the number of moles of CO₂ in 35.2 g
Using the molar mass of CO₂, we can find the number of moles:
\[ \text{Number of moles of CO₂} = \frac{\text{mass}}{\text{molar mass}} = \frac{35.2 \, \text{g}}{44.01 \, \text{g/mol}} \approx 0.799 \, \text{mol} \]

### Step 3: Calculate the heat released for the formation of 35.2 g of CO₂
The heat of combustion of carbon to CO₂ is given as -393.5 kJ/mol. This means that for every mole of CO₂ formed, 393.5 kJ of heat is released. Therefore, the heat released for 0.799 moles of CO₂ can be calculated as:
\[ \text{Heat released} = \text{Number of moles} \times \text{Heat of combustion} = 0.799 \, \text{mol} \times (-393.5 \, \text{kJ/mol}) \approx -314.7 \, \text{kJ} \]

### Step 4: Round the answer
Rounding -314.7 kJ to three significant figures gives us:
\[ \text{Heat released} \approx -315 \, \text{kJ} \]

### Final Answer
The heat released upon formation of 35.2 g of CO₂ from carbon and oxygen gas is approximately **-315 kJ**.

---