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Lignite is a type of brown coal - VCE - SSCE Chemistry - Question 17 - 2023 - Paper 1

Question 17

Lignite is a type of brown coal. When lignite is completely combusted in a power station, 19.0 MJ/tonne of energy is released. The efficiency of the power station is... show full transcript

Worked Solution & Example Answer:Lignite is a type of brown coal - VCE - SSCE Chemistry - Question 17 - 2023 - Paper 1

Step 1

Calculate the total energy required

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Answer

To determine the total energy required from lignite to produce 42.0 MJ of usable energy, we use the efficiency of the power station. The formula for usable energy is:
$E_{usable} = E_{total} \times \text{efficiency}$
Rearranging gives us:
$E_{total} = \frac{E_{usable}}{\text{efficiency}}$
Substituting the values:
$E_{total} = \frac{42.0 \text{ MJ}}{0.39} \approx 107.69 \text{ MJ}$

Step 2

Calculate the mass of lignite required

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Answer

Now, we can find the mass of lignite needed by using its energy content:
$\text{mass} = \frac{E_{total}}{E_{per\ tonne}}$
Where:

$E_{per\ tonne} = 19.0 \text{ MJ/tonne}$
Substituting the values:
$\text{mass} = \frac{107.69 \text{ MJ}}{19.0 \text{ MJ/tonne}} \approx 5.67 \text{ tonnes}$

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