Carbon compounds, thermochemistry, redox and industrial chemistry / Sebatian karbon, termokimia, redoks dan kimia industri
This combined domain tests four linked areas: carbon compounds, thermochemistry, redox and industrial chemistry. Questions often bridge them, for example calculating energy from a fuel or identifying a redox step in an industrial route.
Carbon compounds
Alkanes CnH2n+2 are saturated and undergo substitution with halogens in UV light. Alkenes CnH2n are unsaturated, undergo addition and decolourise bromine water. Alcohols CnH2n+1OH can be oxidised to carboxylic acids and form esters with acids. Carboxylic acids are weak acids and react with metals and carbonates. Addition polymerisation joins monomers with C=C; condensation polymerisation releases small molecules, as in nylon and PET. Isomers share a molecular formula but differ in structure.
Thermochemistry and redox
Exothermic reactions release heat, have negative ΔH and lower-energy products. Endothermic reactions absorb heat and have positive ΔH. Bond breaking absorbs energy; bond making releases energy. In redox, oxidation number rises in oxidation and falls in reduction; the oxidising agent is reduced. Rusting needs oxygen and water; a more reactive sacrificial metal such as Mg or Zn protects iron.
Industrial
Haber process: N₂ + 3H₂ ⇌ 2NH₃, iron catalyst, about 450 °C and 200 atm. Contact process: 2SO₂ + O₂ ⇌ 2SO₃, V₂O₅ catalyst, about 450 °C and 1 atm.
Worked example
50 cm³ of 1.0 mol dm⁻³ HCl is mixed with 50 cm³ of 1.0 mol dm⁻³ NaOH; the temperature rises by 6.5 °C. q = mcθ = 100 g × 4.2 J g⁻¹ °C⁻¹ × 6.5 °C = 2730 J = 2.73 kJ. Moles of water formed = 0.050 mol. ΔH = −2.73 ÷ 0.050 = −54.6 kJ mol⁻¹. Reasoning: use the total solution mass and the limiting mole ratio.
Traps
Do not write ΔH without a sign. In q = mcθ, use the total mass, not the mass of one solution. Oxidation number is not the same as charge for covalent species. The alkene test is decolourisation of bromine water; alkanes do not do this in the dark. Do not confuse rate with equilibrium in Haber and Contact questions.