IB Chemistry HL R1.3 Energy from fuels questions

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Type
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Question 1

Paper 2Easy8 marks

A student compares the air supply to two identical burners, each supplied with methane, CH₄, at the same rate. Figure 1 is a schematic diagram; the side arrows indicate the relative air supply to each burner.

ABCH4CH4
(a)

Using Figure 1, identify which burner is more likely to undergo incomplete combustion. Give one reason based on the figure.

[2]
(b)

For burner B, write a balanced equation for incomplete combustion of methane in which carbon monoxide and water are the products. State symbols are not required.

[2]
(c)

Ethanol, C₂H₅OH, burns with a restricted oxygen supply to form solid carbon and water. Write a balanced equation for this reaction. State symbols are not required.

[2]
(d)

State one health risk of carbon monoxide and suggest one change that would reduce the likelihood of carbon monoxide forming or accumulating.

[2]

Question 2

Multiple choiceMedium1 mark

A 23.0 g sample of bioethanol, C₂H₅OH, is burned completely. Assume all its carbon was fixed from atmospheric CO₂ by recent photosynthesis, and ignore emissions from production and transport. The combustion equation is C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. Use M(C₂H₅OH) = 46.0 g mol⁻¹ and M(CO₂) = 44.0 g mol⁻¹. What are the mass of CO₂ released and the net change in atmospheric CO₂ from fixation and combustion together? Treat an increase as positive.

Show answer and explanation

Answer: C. The equation gives 2 mol CO₂ per mole of ethanol. The ethanol amount is 23.0/46.0 = 0.500 mol, so combustion releases 1.00 mol CO₂ × 44.0 g mol⁻¹ = 44.0 g. The same 1.00 mol of atmospheric CO₂ had been fixed to provide the carbon in the ethanol, so the net change is +44.0 − 44.0 = 0.0 g.

A: uses a 1:1 rather than 1:2 ethanol-to-CO₂ mole ratio, giving 22.0 g. B: calculates the released CO₂ but omits the earlier photosynthetic uptake. D: counts the uptake as a negative change but omits the CO₂ released on combustion.

Remember: for the stated carbon balance, recently fixed carbon returns to the atmosphere on combustion.

Question 3

Paper 2Medium7 marks

A pilot plant produces bioethanol from glucose in crop biomass. Figure 1 shows a simplified carbon pathway for one batch. The fermentation equation is:

\ceC6H12O6−>2C2H5OH+2CO2\ce{C6H12O6 -> 2C2H5OH + 2CO2}

Use relative atomic masses from the data booklet where needed.

Atmospheric CO2Crop biomass:glucoseFermentationBioethanolphotosynthesis;carbon fixed duringone growing season90.0 kg glucose38.6 kg ethanol collectedCO2 releasedcombustion releasesCO2
(a)

Write a balanced equation for photosynthesis in plants.

[1]
(b)

Use the fermentation equation and Figure 1 to calculate the theoretical mass of ethanol and the percentage yield for this batch. Give the mass in kg and the percentage yield to three significant figures.

[3]
(c)

Using Figure 1, explain why the ethanol can be considered a renewable fuel.

[2]
(d)

State one reason why Figure 1 alone does not establish that using this bioethanol is carbon neutral.

[1]

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