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Consider the following information - VCE - SSCE Chemistry - Question 6 - 2007 - Paper 1

Question 6

Consider the following information. • Ethanol burns in excess air according to the following equation. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) ΔH = -1364 kJ mol^-1 ... show full transcript

Worked Solution & Example Answer:Consider the following information - VCE - SSCE Chemistry - Question 6 - 2007 - Paper 1

Step 1

Calculate the minimum amount of energy, in kJ, required to heat 550 g of water and the pot from 18.5°C to 100.0°C.

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Answer

To calculate the total energy required, we must sum the energy needed to heat both the water and the aluminum pot.

Energy for Water:

Using the formula:

$Q = mc riangle T$

where:
- $m$ = mass of water = 550 g,
- $c$ = specific heat capacity of water = 4.18 J g^{-1} °C^{-1},
- $riangle T$ = change in temperature = 100.0°C - 18.5°C = 81.5°C.
$Q_{water} = 550 imes 4.18 imes 81.5 = 198,165 ext{ J} = 198.2 ext{ kJ}$
Energy for Aluminium Pot:

For the aluminum pot, we use the same formula:

where:
- $m$ = mass of aluminum = 150 g,
- $c$ = specific heat capacity of aluminum = 9.000 J g^{-1} °C^{-1}.
$Q_{aluminium} = 150 imes 9.000 imes 81.5 = 1,116,750 ext{ J} = 1116.8 ext{ kJ}$
Total Energy Required:

$Q_{total} = Q_{water} + Q_{aluminium} = 198.2 + 1116.8 = 1315 ext{ kJ}$

Thus, the minimum energy required is approximately 1315 kJ.

Step 2

Calculate the mass, in g, of ethanol that needs to be completely burnt to provide this energy.

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Answer

To determine the mass of ethanol required to provide this energy:

Use the heat of combustion of ethanol:

Given that the heat of combustion for ethanol is ΔH = -1364 kJ/mol.
Calculate the moles of ethanol needed:

Using the formula:

$ext{moles} = rac{Q_{needed}}{ ext{ΔH}} = rac{1315 ext{ kJ}}{1364 ext{ kJ/mol}} = 0.965 ext{ mol}$
Calculate the mass of ethanol:

The molar mass of ethanol (C2H5OH) is 46.07 g/mol.

$ext{mass} = ext{moles} imes ext{molar mass} = 0.965 imes 46.07 = 44.42 ext{ g}$

Thus, 44.42 g of ethanol needs to be burnt.

Step 3

Calculate the mass, in g, of ethanol that needs to be burnt in practice to heat the water and the pot from 18.5°C to 100.0°C.

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Answer

In this part, we take into account that only 35% of the energy released from the combustion of ethanol is effectively used:

Calculate the effective energy released:

$Q_{effective} = 0.35 imes Q_{needed} = 0.35 imes 1315 ext{ kJ} = 460.25 ext{ kJ}$
Calculate the moles of ethanol for effective energy:

$ext{moles} = rac{Q_{effective}}{ ext{ΔH}} = rac{460.25 ext{ kJ}}{1364 ext{ kJ/mol}} = 0.337 ext{ mol}$
Calculate the mass of ethanol burned in practice:

$ext{mass} = ext{moles} imes ext{molar mass} = 0.337 imes 46.07 = 15.53 ext{ g}$

Thus, 15.53 g of ethanol needs to be burnt in practice.

Consider the following information - VCE - SSCE Chemistry - Question 6 - 2007 - Paper 1

Worked Solution & Example Answer:Consider the following information - VCE - SSCE Chemistry - Question 6 - 2007 - Paper 1

Calculate the minimum amount of energy, in kJ, required to heat 550 g of water and the pot from 18.5°C to 100.0°C.

Calculate the mass, in g, of ethanol that needs to be completely burnt to provide this energy.

Calculate the mass, in g, of ethanol that needs to be burnt in practice to heat the water and the pot from 18.5°C to 100.0°C.

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