The enthalpy of combustion of `C_(6)H_(6)` is- 3250 kJ when 0.39g of `C_(6)H_(6)` is burnt in excess of oxgyen in an open vessel, the amount of heat envolved is:

Options

A. 8.32 kJ
B. 12.36 kJ
C. 16.25 kJ
D. 20.74 kJ

Explanation

To solve the problem of calculating the amount of heat evolved when 0.39 g of benzene (C₆H₆) is burned, we can follow these steps:

### Step 1: Understand the Enthalpy of Combustion
The enthalpy of combustion of benzene (C₆H₆) is given as -3250 kJ. This value indicates that when one mole of benzene is burned, 3250 kJ of energy is released.

### Step 2: Determine the Molar Mass of Benzene
To use the enthalpy of combustion, we need to know the molar mass of benzene:
- Carbon (C) has a molar mass of approximately 12 g/mol.
- Hydrogen (H) has a molar mass of approximately 1 g/mol.

Calculating the molar mass of C₆H₆:
\[ \text{Molar mass of C₆H₆} = (6 \times 12) + (6 \times 1) = 72 + 6 = 78 \text{ g/mol} \]

### Step 3: Use the Unitary Method
We know that 78 g of benzene releases 3250 kJ of heat. We need to find out how much heat is released by 0.39 g of benzene.

Using the unitary method:
\[ \text{Heat released by 0.39 g of C₆H₆} = \left( \frac{3250 \text{ kJ}}{78 \text{ g}} \right) \times 0.39 \text{ g} \]

### Step 4: Calculate the Heat Released
Now, we can perform the calculation:
\[ \text{Heat released} = \left( \frac{3250}{78} \right) \times 0.39 \]

Calculating the first part:
\[ \frac{3250}{78} \approx 41.67 \text{ kJ/g} \]

Now, multiply by 0.39 g:
\[ \text{Heat released} \approx 41.67 \times 0.39 \approx 16.25 \text{ kJ} \]

### Conclusion
The amount of heat evolved when 0.39 g of benzene is burned is approximately **16.25 kJ**.

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