Understanding Methane's Higher Heating Value (HHV)

The Higher Heating Value (HHV) represents the total amount of heat released when a fuel is burned completely, assuming the water produced is condensed back into liquid. We need to find the HHV of methane ($\text{CH}_4$) in terms of grams of carbon (gC) per megajoule (MJ) of energy released.

Calculation Steps

1. Identify Given Information:
   • Combustion of 1 mol of $\text{CH}_4$ releases 890 kJ of energy.
   • Combustion of 1 mol of $\text{CH}_4$ produces 1 mol of $\text{CO}_2$.
   • 1 mol of $\text{CO}_2$ contains 12 g of carbon (C).
2. Relate Energy to Carbon Content:

   The combustion of 1 mol of $\text{CH}_4$ releases 890 kJ and corresponds to 12 g of carbon.

3. Convert Energy Units:

   Convert the energy from kilojoules (kJ) to megajoules (MJ), knowing that 1 MJ = 1000 kJ.

   Energy = $890 \text{ kJ} \times \frac{1 \text{ MJ}}{1000 \text{ kJ}} = 0.890 \text{ MJ}$

4. Calculate HHV in gC/MJ:

   Divide the mass of carbon associated with the combustion by the energy released in MJ.

   HHV = $\frac{\text{Mass of Carbon}}{\text{Energy Released}} = \frac{12 \text{ gC}}{0.890 \text{ MJ}}$

   HHV $\approx 13.483 \text{ gC/MJ}$

5. Round the Result:

   Rounding the result to one decimal place gives 13.5 gC/MJ.

Final HHV Value

The higher heating value (HHV) of methane is approximately 13.5 gC/MJ.