Question

Octane (C8H18) burns in oxygen to produce carbon dioxide gas andwater vapour.
Write a balanced chemical equation for this process.
Calculate the volume of carbon dioxide produced at 25°C and apressure of
1.01×105 Pa when 9.85 g of octane is used up in the combustionreaction.
(R = 8.314 J K-1 mol-1; Atomic masses: C = 12.01, H = 1.01, O =15.99)
[8 marks]

(ii) State Henry's Law for the solubility of gases inliquids.
The solubility of O2 in water at 25°C and 1 atm is 3.5×10-4mol/L.
Given that the partial pressure of O2 in air is 0.22 atm, calculatethe concentration of
oxygen dissolved in water under atmospheric conditions.
Explain why the solubility of gases in water decreases at highertemperatures whilst the solubility of most ionic solidsincreases.
[8 marks]

(iii) The combustion of ammonia in the presence of a platinumcatalyst produces nitric
oxide (NO) and water.
Write a balanced chemical equation for this process and brieflydescribe the role of the catalyst.
Calculate the standard enthalpy change for this reaction giventhat:
N2(g) + O2(g) ? 2NO(g); ?H = 180.6 kJ
N2(g) + 3H2(g) ? 2NH3(g); ?H = -91.8 kJ
2H2(g) + O2(g) ? 2H2O(g); ?H = -483.7 kJ
Predict whether the entropy change in this system will be positiveor negative and
comment on the spontaneity of this reaction.
[9 marks]