Photo AI
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 (C₂H₅O... 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 for heating and cooking
Answer
To find the total energy required over 13 weeks:
-
Total energy needed = 13 weeks × 800 MJ/week = 10400 MJ = 1.04 × 10⁹ J
-
The reaction for burning ethanol gives off -1370 kJ/mol. Convert this to J:
-1370 kJ/mol = -1370 × 10³ J/mol = -1370000 J/mol
-
Now, calculate the moles of ethanol needed:
Moles of ethanol needed = Total energy needed / Energy released per mole
= [ \frac{1.04 \times 10^9 \text{ J}}{-1370000 \text{ J/mol}} ]
= 759.1 mol
-
The molar mass of ethanol (C₂H₅OH) is approximately 46 g/mol:
Mass of ethanol = Moles × Molar mass
= 759.1 mol × 46 g/mol = 34920 g = 34.92 kg
Step 2
Step 3
Calculate the electrical energy provided per mole of ethanol consumed in the fuel cell
Answer
-
The voltage across the fuel cell is given as 1.15 V.
-
The total number of moles of electrons transferred per mole of ethanol consumed is 12 (as evident from the half-reaction).
-
The electrical energy provided can be calculated using:
Electrical energy (in J) = Number of moles of electrons × Faraday's constant × Voltage
= 12 mol × 96485 C/mol × 1.15 V
= 1330 J = 1.33 kJ
Step 4