IB Chemistry HL 1.3 Energy From Fuels Questions

Practise IB Chemistry HL Energy from Fuels questions by balancing combustion equations, comparing fuel evidence and interpreting hydrogen or methanol fuel cells.

Exam points

Balance complete-combustion equations for hydrocarbons and alcohols with correct products and coefficients.
Identify CO or carbon in incomplete-combustion equations and distinguish them from complete products.
Compare fossil fuels by CO₂ output and energy yield; explain the greenhouse effect from infrared absorption.
Evaluate biofuels using renewable carbon fixation, energy efficiency and practical fuel trade-offs.
Write hydrogen- or methanol-cell half-equations and identify direct chemical-to-electrical conversion.

Covered syllabus points

1.3.1—Combustion reactions 1.3.2—Incomplete combustion 1.3.3—Fossil fuels 1.3.4—Biofuels 1.3.5—Fuel cells 1.4.1 (HL)—Entropy (S)1.4.2 (HL)—Gibbs energy (ΔG)1.4.3 (HL)—Spontaneity 1.4.4 (HL)—Equilibrium and Gibbs energy

[Maximum number: 2]

Urea, $\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}$ , is excreted by mammals and can be used as a fertilizer.

The combustion of urea produces water, carbon dioxide and nitrogen.

Formulate a balanced equation for the reaction.

$2\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}(\mathrm{~s})+3 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+2 \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{~N}_{2}(\mathrm{~g})$

[Maximum number: 1]

Ethanol is obtained by the hydration of ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

Suggest two possible products of the incomplete combustion of ethene that would not be formed by complete combustion.

[Maximum number: 5]

Ethanol is a biofuel that can be mixed with gasoline.

(a)

Write the equation for the complete combustion of ethanol.

[ 1 ]

$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{l})+3 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$

(b)

Outline the evidence that relates global warming to increasing concentrations of greenhouse gases in the atmosphere.

[ 2 ]

Any two of:

«showing strong» correlation between «atmospheric» $\ce{CO2}$ concentration/greenhouse gas concentration and average «global/surface/ocean» temperature

lab evidence that greenhouse gases/ $\mathrm{CO}_{2}$ absorb(s) infrared radiation «advanced» computer modelling

ice core data

tree ring data

ocean sediments / coral reefs / sedimentary rocks data

Do not accept "global warming" for "average temperature".

Do not accept "traps/reflects heat" OR "thermal energy".

Evidence must be outlined and connected to data.

Accept references to other valid greenhouse gases other than carbon dioxide/ $\mathrm{CO}_{2}$ , such as methane/ $\mathrm{CH}_{4}$ or nitrous oxide/ $\mathrm{N}_{2} \mathrm{O}$ .

(c)

Explain, including a suitable equation, why biofuels are considered to be carbon neutral.

[ 2 ]

biofuel raw material/sugar/glucose formed by photosynthesis

OR

biofuel raw material/sugar/glucose uses up carbon dioxide during its formation OR

biofuel from capturing gases due to decaying organic matter formed from photosynthesis

$6 \mathrm{CO}_{2}(\mathrm{~g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})+6 \mathrm{O}_{2}(\mathrm{~g})$

Accept arguments based on material coming from plant sources consuming carbon dioxide/carbon for M1.

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Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)

Question (c)