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An isolated research station is to be staffed by a small group of scientists for 13 weeks - VCE - SSCE Chemistry - Question 6 - 2002 - Paper 1
Question 6
An isolated research station is to be staffed by a small group of scientists for 13 weeks. Part of the exercise is to test the effectiveness of liquid ethanol (CH₃CH... show full transcript
Worked Solution & Example Answer:An isolated research station is to be staffed by a small group of scientists for 13 weeks - VCE - SSCE Chemistry - Question 6 - 2002 - Paper 1
Step 1
Calculate the total mass of ethanol needed
Answer
To find the total energy required over the 13-week period, we first convert the average weekly requirement to Joules:
Total energy needed = 13 weeks × 800 MJ/week × 10⁶ kJ/MJ = 1.04 × 10⁹ kJ.
Next, we can use the enthalpy change of the reaction to find the moles of ethanol needed:
From the reaction, the ΔH shows that 1 mole of ethanol produces 1370 kJ. Therefore:
Moles of ethanol = ( \frac{1.04 \times 10^9 \text{ kJ}}{1370 \text{ kJ/mol}} \approx 759.1 \text{ mol} )
Lastly, we need to find the total mass of ethanol:
Given the molar mass of ethanol (C₂H₆O) is approximately 46 g/mol:
Mass of ethanol = moles × molar mass = 759.1 mol × 46 g/mol = 34925.6 g, or approximately 34.93 kg.
Step 2
Step 3
Calculate the electrical energy provided per mole of ethanol consumed in the fuel cell
Answer
To find the electrical energy provided per mole of ethanol, we use the voltage given:
Energy = Voltage × Charge
The charge can be found using Faraday's constant (approximately 96485 C/mol). For 4 moles of electrons:
Charge = 4 × 96485 C = 385940 C.
Thus, the electrical energy per mole of ethanol is:
Electrical energy = 1.15 V × 385940 C = 442825 J (or 442.8 kJ).
Step 4
Suggest one important reason why the fuel cell would be better than the generator for this purpose
Answer
One important reason why the fuel cell would be better than the generator is that fuel cells are generally more efficient and produce less pollution compared to internal combustion engines.