Digesters use 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 seam gas contain CH₄ as their main component. Why is biogas considered a renewable energy source but coal seam gas is not? b. A digester processed 1 kg of organic waste to produce 496.0 L of biogas at standard laboratory conditions (SLC). The biogas contained 60.0% CH₄. i. Write the thermochemical equation for the complete combustion of CH₄ at SLC. ii. Calculate the amount of energy that could be produced by CH₄ from 1 kg of organic waste.

SSCE VCE Chemistry Measuring Gases: Digesters use bacteria to conver

Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, CH₄ - VCE - SSCE Chemistry - Question 1 - 2021 - Paper 1

Question 1

Digesters use 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:Digesters use 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?

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Answer

Biogas is considered a renewable energy source because its production relies on the continuous breakdown of organic waste through bacterial action. This cycle allows biogas to be generated repeatedly and sustainably over time. In contrast, coal seam gas is derived from fossil fuels, which take millions of years to form. The extraction and use of coal seam gas therefore occur at a rate that far exceeds its natural replenishment, resulting in a finite supply.

Step 2

Write the thermochemical equation for the complete combustion of CH₄ at SLC.

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The complete combustion of methane can be represented by the following thermochemical equation:

ightarrow ext{CO}_2(g) + 2 ext{H}_2 ext{O}(g)$$

Step 3

Calculate the amount of energy that could be produced by CH₄ from 1 kg of organic waste.

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Answer

To calculate the energy produced, we first determine the amount of CH₄ produced from 1 kg of organic waste:

Total volume of biogas produced: 496.0 L
Volume of CH₄ in biogas: 60.0% of 496.0 L = 0.60 × 496.0 = 297.6 L CH₄

Using the ideal gas law, we can convert this volume to moles (at SLC, 1 mole of gas occupies approximately 24.45 L):

$ext{moles of CH}_4 = \frac{297.6 ext{ L}}{24.45 ext{ L/mol}} \approx 12.18 ext{ moles}$

The energy released from the combustion of 1 mole of CH₄ is about 890 kJ. Thus, the total energy produced from 12.18 moles is:

$ext{Total Energy} = 12.18 ext{ moles} \times 890 ext{ kJ/mole} \approx 10838.2 ext{ kJ}$

Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, CH₄ - VCE - SSCE Chemistry - Question 1 - 2021 - Paper 1

Worked Solution & Example Answer:Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, CH₄ - VCE - SSCE Chemistry - Question 1 - 2021 - Paper 1

Why is biogas considered a renewable energy source but coal seam gas is not?

Write the thermochemical equation for the complete combustion of CH₄ at SLC.

Calculate the amount of energy that could be produced by CH₄ from 1 kg of organic waste.

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