Question

Heat of combustion of liquid benzene to carbon dioxide and water is \(-3266 \, \text{kJ/mol}\). What is the amount of heat liberated when 780 mg of benzene is fully oxidised? (At mass of C = 12, H = 1)

• A. 32.66 kJ
• B. 326.6 kJ
• C. 65.32 kJ
• D. 16.33 kJ

Hint:

To calculate the heat released or absorbed, multiply the number of moles of a substance by its heat of combustion per mole.

Answer 1

The Correct Option is A

Step 1: Molar mass of benzene.
The molar mass of benzene (C$_6$H$_6$) is calculated as: \[ \text{Molar mass of C}_6\text{H}_6 = 6 \times 12 + 6 \times 1 = 78 \, \text{g/mol} \] Step 2: Moles of benzene.
The mass of benzene given is 780 mg = 0.780 g. The number of moles of benzene is: \[ \text{Moles of benzene} = \frac{\text{mass}}{\text{molar mass}} = \frac{0.780 \, \text{g}}{78 \, \text{g/mol}} = 0.01 \, \text{mol} \] Step 3: Heat liberated.
The heat liberated per mole of benzene is \(-3266 \, \text{kJ/mol}\). Therefore, the total heat released for 0.01 mol is: \[ \text{Heat liberated} = 0.01 \times 3266 = 32.66 \, \text{kJ} \] Step 4: Conclusion.
The correct amount of heat liberated is 32.66 kJ, so the correct answer is (A).