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Digester uses bacteria to convert organic waste into biogas, which contains mainly methane, CH₄ - VCE - SSCE Chemistry - Question 1 - 2021 - Paper 1
Question 1
Digester uses bacteria to convert organic waste into biogas, which contains mainly methane, CH₄. Biogas can be used as a source of energy. a. Both biogas and coal s... show full transcript
Worked Solution & Example Answer:Digester uses bacteria to convert organic waste into biogas, which contains mainly methane, CH₄ - VCE - SSCE Chemistry - Question 1 - 2021 - Paper 1
Step 1
Why is biogas considered a renewable energy source but coal seam gas is not?
Answer
Biogas is considered a renewable energy source because it is produced using organic waste, which can be continuously replenished through natural processes. The cycle of decomposition and conversion into biogas can occur rapidly, allowing for ongoing production. In contrast, coal seam gas is extracted from finite geological resources that take millions of years to form and cannot be replenished in a practical timeframe, making it a non-renewable energy source.
Step 2
Step 3
Calculate the amount of energy that could be produced by CH₄ from 1 kg of organic waste.
Answer
To calculate the energy produced from CH₄:
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Determine the amount of CH₄ produced from 1 kg of organic waste:
Biogas produced = 496.0 L (at SLC) CH₄ content in biogas = 60.0%
Volume of CH₄ = 496.0 L × 0.60 = 297.6 L CH₄
Using the ideal gas law, at standard laboratory conditions (SLC), 1 mole of gas occupies 24.45 L:
Moles of CH₄ = ( \frac{297.6 \text{ L}}{24.45 \text{ L/mol}} \approx 12.16 \text{ moles} )
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Use the standard heat of combustion for CH₄:
The heat of combustion of methane is approximately -890 kJ/mol.
Total energy produced = 12.16 moles × -890 kJ/mol ≈ -10810.4 kJ
Therefore, the energy that could be produced from CH₄ from 1 kg of organic waste is approximately 10,810.4 kJ.