Photo AI
The molar heat of combustion of ethanol is 1367 kJ mol<sup>−1</sup> - HSC - SSCE Chemistry - Question 10 - 2008 - Paper 1
Question 10
The molar heat of combustion of ethanol is 1367 kJ mol<sup>−1</sup>. What quantity of ethanol must be combusted to raise the temperature of 1.0 kg water from 50°C t... show full transcript
Worked Solution & Example Answer:The molar heat of combustion of ethanol is 1367 kJ mol<sup>−1</sup> - HSC - SSCE Chemistry - Question 10 - 2008 - Paper 1
Step 1
What quantity of ethanol must be combusted to raise the temperature of 1.0 kg water from 50°C to boiling point at sea level?
Answer
To calculate the amount of ethanol required, we first need to find the heat energy required to raise the temperature of the water.
-
Calculate the heat energy needed (Q): The required temperature change for water is:
100 °C - 50 °C = 50 °C
The heat energy needed can be calculated using the formula:
Where:
- m = mass of the water = 1.0 kg
- c = specific heat capacity of water = 4.18 kJ/(kg·°C)
- θ = change in temperature = 50 °C
Inserting values:
-
Determine moles of ethanol required: With the molar heat of combustion of ethanol being 1367 kJ/mol, the number of moles needed to produce 209 kJ is:
ext{moles} = rac{Q}{ ext{molar heat}} = rac{209 ext{ kJ}}{1367 ext{ kJ/mol}} ext{ moles} ≈ 0.153 ext{ mol}
-
Calculate mass of ethanol required: The molar mass of ethanol (C₂H₅OH) is approximately 46 g/mol. Therefore, the mass of ethanol required is:
Thus, the quantity of ethanol required is approximately 7.0 g.