Question

The enthalpy of combustion of methane is \(-890 \, \text{kJ/mol}\). What is the enthalpy change when 8 g of methane is burned?
(Molar mass = 16 g/mol)

• A. \(-890 \, \text{kJ}\)
• B. \(-445 \, \text{kJ}\)
• C. \(-222.5 \, \text{kJ}\)
• D. \(-556 \, \text{kJ}\)

Hint:

Use the relation: \(\Delta H = n \times \Delta H_{\text{molar}}\), where \( n \) is moles and \(\Delta H_{\text{molar}}\) is the molar enthalpy change.

Answer 1

The Correct Option is B

Step 1: Given enthalpy of combustion of methane (\(\Delta H_c\)) for 1 mole = \(-890 \, \text{kJ/mol}\). 
Molar mass of methane (CH\textsubscript{4}) = 16 g/mol.
Step 2: Calculate the number of moles in 8 g of methane: \[ n = \frac{\text{mass}}{\text{molar mass}} = \frac{8}{16} = 0.5 \, \text{mol} \]
Step 3: Calculate the enthalpy change for 0.5 mole: \[ \Delta H = n \times \Delta H_c = 0.5 \times (-890) = -445 \, \text{kJ} \]
Step 4: Therefore, the enthalpy change when 8 g of methane is burned is \(-445 \, \text{kJ}\).