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 seam gas contain CH₄ as their main component. Why is biogas considered a renewable energy source but coal seam gas is not?
Solution

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.

Solution

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

Solution

c. Biogas was combusted to release 1.63 × 10³ kJ of energy. This energy was used to heat 100 kg of water in a tank. The initial temperature of the water was 25.0 °C.

i. What is the maximum temperature that the water in the tank could reach?

ii. State why this temperature may not be reached.

Solution

2. Which one of the following statements is correct?

A. Pentane has a higher flashpoint than octane.
B. The flashpoint of all the structural isomers of C₄H₁₀O are equal.
C. The higher the flashpoint of a compound, the higher its fire risk.
D. The flashpoint of all the optical isomers of 3-methyl hexane are equal.

Solution

3. 1L of octane has a mass of 703 g at SLC. The efficiency of the reaction when octane undergoes combustion in the petrol engine of a car is 25.0%. What volume of octane stored in a petrol tank at SLC is required to produce 528 MJ of usable energy in a combustion engine?

A. 3.92 L
B. 11.8 L
C. 15.7 L
D. 62.7 L

Solution