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Since the start of the industrial age, most of the energy used by humans has come from the burning of coal and oil - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1
Question 9
Since the start of the industrial age, most of the energy used by humans has come from the burning of coal and oil. In that time the amount of CO₂ in the air has inc... show full transcript
Worked Solution & Example Answer:Since the start of the industrial age, most of the energy used by humans has come from the burning of coal and oil - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1
Step 1
a. Calculate the additional mass of CO₂ in kg
Answer
To find the additional mass of CO₂, we need to calculate the difference in the percentage of CO₂ in the atmosphere:
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Calculate the change in CO₂ percentage:
0.58 ext{%} - 0.42 ext{%} = 0.16 ext{%}
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Convert this percentage to a mass:
m(CO₂) = 0.16 ext{%} imes 5.15 imes 10^{18} ext{ kg}
= rac{0.16}{100} imes 5.15 imes 10^{18} = 8.24 imes 10^{15} ext{ kg}
Therefore, the additional mass of CO₂ added to the atmosphere is approximately 8.24 × 10¹⁵ kg.
Step 2
b. Calculate the total amount of energy produced
Answer
Given that half of the additional CO₂ comes from burning coal, the mass of coal burnt is:
m(C) = rac{m(CO₂)}{2} = rac{8.24 imes 10^{15}}{2} = 4.12 imes 10^{15} ext{ kg}
Next, we will calculate the number of moles of carbon:
n(C) = rac{m(C)}{M(C)}
Where M(C) = 12 g/mol. Converting kg to g:
n(C) = rac{4.12 imes 10^{15} ext{ kg} imes 1000}{12} = 3.43 imes 10^{16} ext{ mol}
Using the enthalpy change for combustion, the energy produced is:
E = n(C) imes ext{ΔH} = 3.43 imes 10^{16} ext{ mol} imes (-394 ext{ kJ mol}^{-1})
Therefore:
E = -1.35 imes 10^{19} ext{ kJ}