IBDP Chemistry -Reactivity 1.3 Energy from fuels - IB Style Questions For SL Paper 2 -FA 2025

(a)(i)
The balanced equation for photosynthesis is:
\( 6\text{CO}_2(g) + 6\text{H}_2\text{O}(l) \rightarrow \text{C}_6\text{H}_{12}\text{O}_6(aq) + 6\text{O}_2(g) \)
\(\boxed{6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2}\)

(a)(ii)
Any two of the following advantages:
1. Renewable/Sustainable: Ethanol is produced from plant biomass, unlike finite fossil fuels. ✓
2. Lower Carbon Footprint: The CO₂ released during combustion is roughly equal to the CO₂ absorbed by the plants during growth, making it closer to carbon neutral. ✓
3. Reduced Sulfur Emissions: Produces less sulfur dioxide, leading to less acid rain compared to gasoline. ✓
4. Biodegradable/Less Toxic: Generally less harmful to the environment if spilled than gasoline. ✓
Two valid advantages.

(b)
1. Find the energy released from combusting 4.00 g of ethanol.
• Molar mass of ethanol (C₂H₅OH) = (2×12.01) + (6×1.01) + 16.00 = 46.08 g mol⁻¹
• Moles of ethanol = \( \frac{4.00}{46.08} = 0.0868 \, \text{mol} \)
• From data booklet (Section 14), the standard enthalpy of combustion of ethanol (ΔH°c) is –1367 kJ mol⁻¹.
• Energy released, Q = \( 0.0868 \times 1367 = 118.6 \, \text{kJ} = 118600 \, \text{J} \) ✓
2. Calculate the temperature increase of the water.
• Mass of water = 500.0 g (since density of water ~1 g cm⁻³)
• Specific heat capacity of water (from data booklet, Section 2), c = 4.18 J g⁻¹ K⁻¹
• Using Q = mcΔT
• \( \Delta T = \frac{Q}{mc} = \frac{118600}{500.0 \times 4.18} = 56.8 \, \text{K} \) ✓
\(\boxed{56.8}\) K (or °C)