Coke, which is essentially pure carbon, is widely used as a fuel. Its complete combustion can be represented by the following equation. C(s) + O2(g) → CO2(g) ΔH = -393 kJ mol⁻¹ However, under certain conditions, the combustion is incomplete and the following reaction also occurs. 2C(s) + O2(g) → 2CO(g) ΔH = -232 kJ mol⁻¹ Calculate the energy, in kJ, released when 2.00 tonne (1 tonne = 10⁶ gram) of coke is reacted with oxygen if 80% of the coke is oxidised to carbon dioxide and the remaining 20% is oxidised to carbon monoxide.

SSCE VCE Chemistry Measuring Changes in Chemical Reactions: Coke, which is essentially pure

Coke, which is essentially pure carbon, is widely used as a fuel - VCE - SSCE Chemistry - Question 3 - 2005 - Paper 1

Question 3

Coke, which is essentially pure carbon, is widely used as a fuel. Its complete combustion can be represented by the following equation. C(s) + O2(g) → CO2(g) ΔH = -... show full transcript

Worked Solution & Example Answer:Coke, which is essentially pure carbon, is widely used as a fuel - VCE - SSCE Chemistry - Question 3 - 2005 - Paper 1

Step 1

Calculate the moles of coke

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Answer

The mass of coke is 2.00 tonnes, which converts to grams:

$2.00 ext{ tonnes} = 2.00 imes 10^6 ext{ g}$

To find the moles of coke, we use the molar mass of carbon, which is approximately 12 g/mol:

$n = rac{m}{M} = rac{2.00 imes 10^6 ext{ g}}{12 ext{ g/mol}} = 1.67 imes 10^5 ext{ mol}$

Step 2

Calculate energy for 80% oxidation to CO₂

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Answer

80% of the coke is oxidised to carbon dioxide:

$ext{Moles of } CO₂ = 0.80 imes 1.67 imes 10^5 ext{ mol} = 1.33 imes 10^5 ext{ mol}$

Using the enthalpy change for the reaction:

$ext{Energy from } CO₂ = 1.33 imes 10^5 ext{ mol} imes (-393 ext{ kJ mol}^{-1}) = -5.24 imes 10^7 ext{ kJ}$

Step 3

Calculate energy for 20% oxidation to CO

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Answer

20% of the coke is oxidised to carbon monoxide:

$ext{Moles of } CO = 0.20 imes 1.67 imes 10^5 ext{ mol} = 0.33 imes 10^5 ext{ mol}$

Using the enthalpy change for the reaction:

$ext{Energy from } CO = 0.33 imes 10^5 ext{ mol} imes (-232 ext{ kJ mol}^{-1}) = -7.66 imes 10^6 ext{ kJ}$

Step 4

Calculate total energy released

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Answer

Total energy released is the sum of energy from both reactions:

$ext{Total Energy} = -5.24 imes 10^7 ext{ kJ} + (-7.66 imes 10^6 ext{ kJ})$

Calculating this gives:

$ext{Total Energy} = -6.00 imes 10^7 ext{ kJ}$

Coke, which is essentially pure carbon, is widely used as a fuel - VCE - SSCE Chemistry - Question 3 - 2005 - Paper 1

Worked Solution & Example Answer:Coke, which is essentially pure carbon, is widely used as a fuel - VCE - SSCE Chemistry - Question 3 - 2005 - Paper 1

Calculate the moles of coke

Calculate energy for 80% oxidation to CO₂

Calculate energy for 20% oxidation to CO

Calculate total energy released

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